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GAGES, GAGING

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GAGES, GAGING

AND

INSPECTION

A COMPREHENSIVE TREATISE COVERING THE
LIMIT SYSTEM, MEASURING MACHINES, AND
MEASURING TOOLS AND GAGES FOR ORIGINAT-
ING AND COMPARING MEASUREMENTS IN THE
MANUFACTURING AND INSPECTION DEPART-
MENT^, INCLUDING MEANS FOR MEASURING
AND INSPECTING SCREW THREADS AND GEARS

1^'

\ BY

DOUGLAS T. HAMILTON, A.S.M.E

AuTBOK OF " Automatic Solsw MACHnncs," " Shrapnel Sbxll

Manufacture," "Cartridge Manufacture/'

"Machxme Foroino," Etc.

FIRST EDITION

NEW YORK

THE INDUSTRIAL PRESS

London: THE MACHINERY PUBLISHING CO., Ltd.

I918

* ■*

' t

i - ■ ■ - 'J

ASTOR, LENOX AND
TILDI-.N fCLNDAllON
I? 1918 L

THE INDUSTRIAL PRESS
NEW YORK

COMPOSITION AND ELECTROTYPING BY F. H. GILSON COMPANY, BOSTON, U. S. A.

. 1 ■

* *

• • »

PREFACE

The development of interchangeable manufacture has made
necessary a complete revolution in the gaging and inspection
systems employed in the mechanical industries. The intro-
duction of the limit system in manufacturing has changed many
of the methods previously in vogue. The intensive manufacture
of arms and ammunition during the past few years has also more
than ever indicated the necessity of accurate and reliable means
of gaging and inspection. No book has been published in the
past dealing exclusively with this subject, nor dealing compre-
hensively enough with it to meet the requirements at the present
time, and for this reason the present volume has been prepared
with a view to cover the principles and the practical application
of the limit system of interchangeable manufacturing, and to
describe the principal tools and gages that are employed in this
work in leading manufacturing establishments in the country.

The principles of the limit system are first dealt with, and then
the different kinds of measuring machines and reference and
working gages are illustrated and described. Gages of many
different tj^es are included — plug and ring gages, profile gages,
indicating gages, thread gages, and devices for measuring gears
of different kinds. The book should, therefore, appeal to those
responsible for the output of shops manufacturing on the inter-
changeable plan, inspectors, foremen, designers of special measur-
ing tools, toolmakers, and others whose duties are in one way or
another connected with the problems of interchangeable manu-
facture, the gages used, and the inspection methods required.

The Author.

New York, February ^ 19 18.

CONTENTS

Chaptek I

REFERENCE STANDARDS AND MEASURING MACHINES

PAon

Standard Unit of Length — Johansson Reference Blocks
— Bench Micrometer Caliper — Measuring Machines —
Automatic Comparator — Interferometer 1-27

Chapter II

LIMITS AND TOLERANCES

Limit System — Allowances for Various Classes of Fits

- Methods of Giving Limits on Drawings 28-46

Chapter III

REFERENCE, WORKING, AND INSPECTION GAGES

Tolerances on Reference Gages — Tolerances on Working
and Inspection Gages — Life of Plug, Ring, and Snap
Gages — Wear of Gages — Material used for Gages —
Types of Gages — Built-up Limit Gages — Taper Gages
— Making Limit Gages 47-88

Chapter IV

PROFILE GAGES

Templet Gages — Progressive or Combination Gages

- Gaging Rifle Parts 89-105

• •

VIU CONTENTS

Chapter V
INDICATING GAGES

Pages

Types of Indicating Gages — Multiplying Lever Indi-
cating Gages — Minimeter — Dial Indicators — Microm-
eter Indicating Gages — Three-point Indicating Gages —

— Star Gages — Height and Depth Gages — Thickness
Gages — Concentricity Gages — Cam and Camshaft Gages

— Gaging and Inspecting Balls and Ball Bearings — Box
Inspection Fixtures — Gaging Watch Escapements 106-197

Chapter VI
GAGING AND INSPECTING SCREW THREADS

Tolerances — Reference Thread Gages — Pipe Threads

— Thread Micrometers — Wire System of Measurements

— Lead of Screw Threads — Angle of Thread — Thread
Limit Gages — A. S. M. E. Gaging Devices — Projection
Method 198-253

Chapter VII

GAGING AND INSPECTING GEARS

Bevel Gear Blanks — Gear-tooth Caliper — Tolerances
and Center Distances — Gear-testing Fixtures — MacCord
Odontoscope 254-283

GAGES, GAGING AND INSPECTION

CHAPTER I

REFERENCE STANDARDS AND MEASURING

MACHINES

In measuring work, many different appliances are used, the
kind of measuring tool depending upon the accuracy required.
For instance, in ordinary machine work, the bow caliper and
scale are used to a large extent for making diameter and length
measurements. When the work calls for a greater refinement,
the micrometer caliper, vernier caliper, micrometer depth gage,
etc., are applied. When still greater accuracy is demanded,
measuring machines are used. For angular measurements,
squares, bevel protractors, and templets are employed.

Standard Unit of Length. — The international meter is the
fundamental unit of length in the United States. The original
standard is retained by the International Bureau of Weights
and Measures, near Paris, France. Several copies of this
primary standard were made in 1889 for the United States and
other governments under the direction of the International
Committee representing the various countries which support
the bureau. The Bureau of Standards, Washington, D. C,
has two copies of the original meter; one — No. 27 — is kept
sealed in a metal case in a fireproof vault, and the other —
No. 21 — is used occasionally to verify the working standards.
The legal equivalent of the meter for commercial purposes
was fixed by law, in 1866, as 39.37 inches. The United States
Bureau 6i Standards was authorized by executive order, in
1893, ^o derive the yard from the meter by the use of this rela-
tion. Metric length measures tested by this bureau are stand-
ardized at 20 degrees C, and standards in the customary

2 GAGING AND INSPECTION

units of yards, feet, and inches are made to be correct at 62
degrees F.

Reference Standards. — In order to check various measuring
instruments, micrometer calipers, standard and special gages,
etc., diflferent types of reference rods and blocks have been
devised. These are very carefully seasoned and lapped, and
are usually supplied in sets varying from blocks of the thick-
ness of feelers to rods several feet in length. Fig. i shows
several types of reference blocks, disks, and rods. The block
shown at A is made from steel, hardened and ground, with

STANDARD 12

IQP

QSPl

Mnrhincrif

Fig. I. Standard Reference Blocka, Disks, and End-measuring Rods

cylindrical ends, and is used for setting micrometers and other
adjustable measuring tools; B shows another type of block
which is particularly adapted for setting the adjustable points
of limit gages. A disk type of standard which is used prin-
cipally for setting micrometer calipers is shown at C, while a
standard block used both for setting gages and for general
tool-room purposes is shown at D, At E is shown a standard
end-measuring rod which is made with rounded ends having a
radius equal to that which the rod is intended to measure.
These rods are made § inch in diameter for lengths of from 3

^ MEASURING MACHINES 3

to 6 inches, and J inch in diameter for lengths of from 6 to i6
inches. At F is shown another t>'pe of standard reference rod
which is made from round steel rods, hardened, ground and
lapped on the ends. To prevent expansion due to handling
when in use, the center portion of the rod is fitted with a sleeve
of heat-insulating material.

Johanssoa Reference Blocks. — The Johansson system of
reference. blocks was originally designed to be used in the tool-
room for quickly laying out and checking gages and fixtures.
Owing to the extreme accuracy to which these blocks are made,
however, tlicy are also used as reference gages, both for manu-

1 MlililSl 1
f JffffllllllllllllllllMl \

::;ifK«ii8i9iMiiiiiiui \
;;ffflllfflllim«

ammwmmmwmm

Fig. 1. JohRnsMO Reference Blocks ■

facturing and for inspection purposes. Fig. 2 shows one set ^^
of these blocks. The combination consists of a series of rec- ^|
tangular blocks, which arc made from nickel steel, carefully ^|
machined, seasoned, ground and lapped on all sides. The ^|
opposite sides of each block are parallel, and the distance be- ^|
tween them is equal to the dimension stamped on them within ^H
a maximum tolerance of 0.00001 inch per inch. These blocks ^1
are supplied in various sets, set No. i, shown in Fig. 3, com-
prising eighty-one blocks, divided into four series. The first
series contains nine blocks, which vary in thickness from o.iooi ^H
to 0.1009 hich, increasing by o.oooi inch increments. The ^|
second series contains forty-nine blocks, which vary in thick- ^H

GAGING AND INSPECTION

I ness from o.ioi to 0.149 inch, increasing by o.ooi inch. The
third series comprises nineteen blocks, varying in thickness
from 0,050 to 0.950 inch, increasing by 0.050 inch increments;
and the fourth series consists of four blocks of i, 2, 3, and 4
inches. This set gives aU the sizes from 0,200 inch up to 11
inches by increments of 0.0001 inch. When furnished with
standard plugs and holder for retaining these blocks, over
100,000 different internal and externa! gages are obtained. The
range can be increased by adding other series of blocks up to
20 inches, and increments in quarter thousandths can be ob-
tained by adding two blocks, 0.10025 and 0,10075 inch.

These blocks are generally used by building them up to
obtain the required size, and owing to the almost perfect flat-
ness of the surfaces, they can be wrung together with sufficient
pressure so that the total number in the set (eighty-one) can
be built up. The contacting surfaces are carefully cleaned
with chamois skin, and then the gages are slid over each other
with a slight pressure. To illustrate how these blocks are used
in combination to obtain any desired size, assume that it is
necessary to measure 3.3625 inches. This can be done by
using four blocks: 3.000, 0.140, 0.122, and 0.1005 '^ich. Other
combinations can also be used for the size given. These blocks
can also be extensively used for setting and checking limit
gages. With the set of eighty-one blocks, any limit gage having
a tolerance as small as 0.0001 inch, from 0.200 inch up to over
II inches, can be checked.

Bench Micrometer Cali{)er. — One of the simplest types of
measuring instruments which comprises the principle of the
micrometer screw and graduated sleeve is shown in Fig. 3.
This is known as a " bench micrometer caliper " and is used
on the bench for taking fme measurements from o to 6 inches.
It is provided with two interchangeable measuring heads, the
one shown on the instrument being graduated to read to o.oooi
inch directly from the thimble, and the other shown at A being
provided with a ten-pitch screw and graduated to read to 0.001
\ inch. The thimbles are 4 inches in diameter, and consequently
I liave coarse graduations, enabling accurate readings to be

MEASURING MACHINES

quickly taken. The adjustable anvil is set by standard refer-
ence blocks. The screw on the thimble has a movement of
1 inch.

Principle of Measuring Machines. — Measuring machines gen-
erally comprise both a vernier scale and a micrometer screw
and wheel. Usually the vernier scale is attached to the bed of
the instrument and is used for setting the headslock bracket
carrying one anvil; the headstock also carries the graduated
wheel operating the spindle through a screw. There are three
important points to consider in designing a measuring machine:
First, to produce an accurate screw, vernier, and wheel; second,

Fit. 3- Bftocb Tjrpe of MeMoring H*cUd«

to secure the proper proportions and rigidity of the bed; and
third, to provide some means of indicating the pressure exerted
on the work placed between the measuring points.

While all three points arc highly important, the third one is
probably the most important and the one that should receive
the most careful attention. A measuring machine not provided
with a pressure indicating device b only of value in the hands
of an expert, and it is practically impossible for two men to
obtain exactly the same readings. Pressure indicating devices
are made in several forms, such as feeler plugs which drop out
from between points when a certain pressure is reached; levels
which are inclined at an angle when acted upon by the moving

GAGING AND mSPECTION

anvil; spring-operated plungers, in conjunction with a scale
and hair-line microscope; and graduated glass tubes into which
a colored liquid is forced by the pressure of a diaphragm con-
nected to the movable anvil.

Brown & Sbarpe Measuring Machine. — The measuring ma-
chine designed and used by the Brown & Sharpe Mfg. Co. for
testing the accuracy of standard gages and other tools that
must be finished to very accurate dimensions is shown in Fig. 4.
This machine belongs to that class of measuring instruments
in which the measurement is made by means of a moving scale
under a. microscope, used in conjunction with a micrometer

Fig. 4. Stown & Sbarpe Measuring Micbine

screw and vernier. The most important feature of this machine
is that all measurements arc made directly from the scales, and
dependence is not placed upon standard test pieces that have
been previously measured by other means.

This measuring instrument consists of a heavy bed A made
of double I-beam section about 4 feet long and 1^ foot deep.
The I-beam section combined with the weight of the bed gives
the machine great rigidity to resist any tendency to deflect
when the anvils or measuring points B and C are brought into
contact with the piece to be measured. The carriage D on the
left-hand side of the bed supports bar E wliich carries the

MEASURING MACHINES 7

graduated scale. This carriage is moved by adjusting screw F,
and clamped by handle G. Bar E is provided with coarse and
fine graduations, and its central portion, whiqh carries the
graduated scale, is cut away, thus placing the scale in a line
with the axis of the measuring points. The guide H which fits
in a slot in the lower surface of the bar holds it rigidly in position.
The carriage / on the right-hand end of the machine supports
the micrometer adjustment J.^ This carriage is regulated by
an adjusting screw K and clamped by handles L. Measuring
points B and C are integral parts of the cylindrical bar and
micrometer screw, respectively. The slide M, supported parallel
to the bar E by the uprights N, carries the microscope O.
Screw P is used to adjust the microscope along the slide. Up-
right Q holds the reading magnifying glass R that facilitates
taking readings on the micrometer vernier.

The scale on the bar £ is 8 inches long and is attached to a
flat surface. It has two lines of graduations, each division
being 0.025 inch. One line of graduations, which is easily
visible to the naked eye, is used for locating the scale approxi-
mately. The other graduations, which are invisible to the
naked eye except under favorable light conditions, are used
for the exact reading of the scale by means of the microscope
0, The lines of these graduations are o.oooi inch wide, being
the same width as the hair line of the microscope; thus the
two lines can easily be brought to coincide. The machine can
be set to measure distances up to 16 inches long.

The micrometer wheel J is graduated to read to 0.0001 inch,
and the vernier plate S used in connection with the wheel
makes it possible to obtain readings as fine as o.ooooi inch.
The wear of the micrometer screw is negligible, inasmuch as
the micrometer readings are only used for short distances and
the wheel never moves more than half a turn. The accuracy
of this screw is also greatly increased by providing it with a
bearing practically equal to its length.

Method of taking Measurements. — To measure an object,
slide D carrying bar E is moved to the right so that the meas-
uring point B will touch the micrometer point C. The micro-

8 GAGING Mm INSPECTION

scope is then set over one line of the scale, generally the zero
line, and the slide is moved to the left until the nearest gradu-
ation of the required size is reached. This is indicated by
bringing the line of the scale under the hair line of the micro-
Bcope. The slide is then fastened.by clamping handle C. Read-
ings less than 0.025 inch are indicated by the micrometer screw
and dial J. The object to be measured is inserted between the
measuring points B and C, and by adjusting the micrometer
screw, the size can be indicated to o.ooooi inch.

^ 1 IHa Jtev*^

Fig. S- Pi*tt & Whitney Me>BuriDE M*chin<i

The accuracy of ihis machine rests fundamentally upon the
iccurate graduations on the scale and the iierfection of the
micrometer screw. Among other factors that contribute to
Jie accuracy of the machine are the weight of the bed and
Jie rigidity of the carriages that support the measuring in-
truments. All bearings and wearing surfaces are scraped ac-
urately to reduce any possible error. The machine is also
irmly braced. As an example of the accuracy of this machine,
t might be mentioned that a pull of about from fifty to seventy-
ive pounds on the bed directly beneath the measuring points
s suCBdent to make a plug J inch in diameter drop out from

MEASCRINC MACHINES 9

between the measuring points. Another test which shows the
sensitiveness of the machine consists in placing the hand on
the bed between the slides and holding it there for approximately
one minute ; the heat of the hand causes the plug to drop from
the measuring points. It is estimated that it requires about
twenty minutes for the machine to regain its "equilibrium" and
overcome the influences exerted by the pull or temperature test.
Pratt & Whitney Measuring Machine. - The Pratt & Whit-
ney measuring machine shown in Fig. 5 employs what is known

JlUk

as a "feeler plug" for determining the pre.S5ure between the
measuring points, thus eliminating the himaan element. This
machine consists of a heavy cast-iron bed provided with ways
upon which two heads are mounted. One head A is normally
fixed to the bed; the other head B is adjustable and is located
along the bed by means of a microscope C and measuring points
D, consisting of plugs provided with fine lines that are spaced
exactly one inch apart. Each head carries a ^indle or meas-

GAGING AND INSPECTION

uring point E and F, and the parts to be measured arc sup-
ported between these spuidles upon rests, or held in the hand,
if very small. Measurements up to one inch are obtained by
means of a large graduated index wheel G, a scale and pointer
at E being provided for approximate setting. This is more
clearly shown in Fig. 6; scale J has twenty-five graduations
representing a movement of the spindle of i.ooo inch, and
pointer K has a single setting line. For measurements greater
than one inch, the sliding head B is set by means of a standard
bar / located at the rear of the machine. This bar carries a
series of plugs D which are provided with graduations exactly
one inch apart and so fine that they are imperceptible to the

naked ej'e. The screw of the sliding-head spindle, by means
of which the adjustments for fractional parts of an inch are
obtained, has twenty-five threads per inch, and the index wheel
has 400 graduations. Therefore, each graduation represents
("Jt °f 2^s inch, or 0.0001 inch. These divisions can be split
up by estimating, making possible the reading of accurate
measurements to o.ooooa inch wdth little difficulty.

In order to insure proper contact between the measuring
points of the instrument, the machine is provided with an in-
dicating de\'ice on the fixed head A. This consists, as shown
in Fig, 7, of two auxiliary jaws L and M, between which a
small J-inch diameter plug .V is held by the pressure of a light

MEASURING ItfACHINES 1 1

helical spring which operates the sliding spindle to which one
of the jaws is attached. The tension of this spring is so adjusted
that, when the measuring points are not in contact, the jaws
will hold the plug A' by friction in the position shown to the
left in Fig. 7. When the measuring points are in contact with
one another 01 with the work being measured) the tension on
this helical spring is slightly reduced, and the plug N swings
down to a position between the jaws, as shown to the right of
the illustration. Should there be an excess pressure between
the jaws, the plug would drop out. Hence, the contact for all
measurements should be just enough to cause plug N to swing
down, but not to drop out. It is estimated that the meas-
urable difference between the faces of the measuring spindles
when the feeler plug is in the -upper and lower positions is

In taking a measurement, the machine should first be set
to the zero position with the measuring points in contact.
This is done by adjusting the screw of the linear scale at the
top of the head to zero and setting the pointer of the index
wheel G nearly to zero. Then the head is slid along the bed
until the measuring faces are almost in contact. For the last
adjustment, screw 0, Fig. 6, is operated until the feeler plug
iV, Fig. 7, shows a tendency to move to the horizontal posi-
tion. The head Is now clamped firmly in position and the
index wheel adjusted until tlie plug swings to a vertical posi-
tion. Then the adjustable index pointer is set to zero and
the line in the eye-piece of the microscope is set so that it
exactly coincides with the zero line of the graduated reference
bar / at the rear of the machine. The adjustment of the line
in the eye-piece is made by means of the screw P. The machine
is now set to the zero position, and, when adjusting the head
for the required measurement, care must be taken not to dis-
turb the eye-piece of the microscope. To measure from zero
to one inch, the micrometer screw can be used directly, but,
for a greater dimension, the sliding head must be located by
means of the microscope so that the line in the microscope is
set exactly on the nearest graduation on the plugs on bar /.

GAGING AND INSPECnON

I Assuming that it is necessary to take a measurement of 12.2508
inches, slide the movable head B along the bed until the micro-
scope is brought directly in line with the 1 2-inch graduation
on bar /. The screw is now turned back until the scale and
index wheel of the adjustable spindle show a movement of
0.2508 inch. As the pitch of the screw is 3^5 inch, a complete
turn of the index wheel equals 0.040 inch. Hence, for a move-

' ment of 0.250S inch, the number of turns of the index wheel
would be six full turns and 108 divisions. The Pratt & Whitney
measuring machines are graduated for English measurements
at 62 degrees F., and in sizes of from 12 to 144 inches.

Rg. S. SloGomb Measuiiug Macbiae

Slocomb Measuring Machine. — The type of measuring ma-
chine used by the J. T. Slocomb Co. is shown in Fig. 8. This
machine is of comparatively simple construction, and consists
of a bed carrying two heads. The heads are of circular section
and slide in a V-groove in the bed, and when set in the required
position are clamped by a C-clamp, as shown. This machine
I is used principally for duplicating measurements by using
master end-measuring rods for setting. The screw has
threads per inch, and the dial is 5 inches in diameter and reads
to o.oooi inch.

The most interesting part of this measuring machine is the
I device for indicating the pressure exerted between the meas-
I uring points. When taking measurements to 0.0001 inch with

MEASURING MACHINES

an ordinary micrometer, it is difficult to determine just what
pressure is being applied on the work; and two inspectors
seldom obtain the same reading. This pressure indicating de-
vice, which is shown in detail in Fig. 9, eliminates the human
factor in taking accurate measurements. In Fig. 9, A repre-
sents a section through the tailstock to which the device is
attached, and B is the plunger anvil which is retained in bush-
ings. This anvil is made a nice sliding fit in the bushings,
and is kept against the front bushing by means of the spring
C. The movement of the anvil is limited by means of the pin

F driven into the collar and working hi an elongated slot in
the tailstock A. The rear end of the anvil B is pointed to an
angle of 60 degrees and rests against a flat portion on pin E
which is retained in the lower end of lever G. Pin £ is ful-
cnmied on two cone-pointed screwsj as shown in the view to
the left, and its axis is located -^ inch below the point of the
plunger. The ratio between the short and long arms of the
lever is -^ to 4 inches, so that, when anvil B moves 0.0001
inch, the top part of lever G moves 0.0064 inch. The top part
of lever G bears against the plunger of the dial indicator H, and
the indicator hand moves about | inch when the plunger or

^^^R^^ GAGING AND INSPECTKJN ^^^^^^^H

^^V anvil B is moved o.oooi inch. A test made in connection H
^^^ with this instrument showed that the heat from three fingers H
of the hand applied for a few seconds to a 4-inch end-mcEisuring H
rod, -/'fl inch in diameter, was sufficient to move the hand of ^|
the dial indicator \ inch. In testing two pieces with this in- j^k
strument, the needle will stand at zero when they are of the ^|
same length. If the needle moves from zero, it indicates that ^1
there is a variation between the lengths of the two pieces.

L^^-^ii^

RU» •" ■«

~-_^.

c
i

5
t
C

Fig. 10. Swils Type ol Measuring Machine

Swiss Measuring Machine. — A measuring machine whici
iffers somewhat in principle from those previously describee
s shown in Figs. 10 and 11. This machine is built by the
jodete Genevoise, Geneva, Switzerland. It is provided witl
wo hair-line microscopes A and B. Microscope A is used fo
fitting movable head C when taking measurements of o\'e
wenty-five millimeters. This microscope is provided witl
Toss-hairs which are brought in line with the graduated marks
in a scale located at the rear of the instrument. This scale

1 MEASURING MACHINES 15

1 510 millimeters long and is graduated in miiiimcters. Micro
cope B is used for determining the position of spring plunge
3, which governs the pressure exerted on the work. Head £
s fastened rigidly to the base and carries the stationary anvi
V, which can be adjusted in case of wear. Spindle D is belt
in a sleeve H, the movement of which is controlled by a screw
jf J-miUimeter pitch, and which is attached to the graduatet
wheel /. Located behind spindle D is a light spring capable
of exerting a pressure on the work of one pound per square
inch.

In setting the machine for measurements of more than twenty
five millimeters, head C is sH<! along the bed unUI both anvils

. li

^ti^^

\: ^'^^il.;;^.:

.^^M

■

»(. It. aoie inew of Machine in Fig. to showing GcaduUed Wheel
•nd Vernior Sc«le

ntact with sufficient pressure so that the line on the sliding
indie is exactly central between the two cross-hairs in micro
ope B, the graduated wheel / at the same time being se
zero. The head is now moved back to approximately the
itance required, using the coarsely graduated brass scale a
e rear, and is clamped by handle A', Fig. 10. Screw L is
hen adjusted until the cross-hairs in (he telescope A exactly
oincide wnth the required graduation on the scale at the rear
The machine is now set to the dimension required. To deter-

GAGING AND INSPECTION

mine the accuracy of the piece being measured, it is located
belweeii the measuring points and the position of the line in
the movable spindle noted; if this is not exactly in the center
of the two cross-hairs in telescope B, wheel /, which is divided
into 500 parts giving direct readings to 0.001 millimeter, is
rotated until the line is directly in the center of the two hair
lines. The amount that wheel / has been moved away from
the zero point indicates the amount that the part varies from
the required size in thousandths of a millimeter.

Kewall MeaBuiing MacIiiDe

Newall Measuring Machine. — The measuring machine built
by the Newall Engineering Co. of Walthamstow, London,
England, is suited for general employment in tool-rooms and
workshops. It permits of making very fine measurements, and
is simple in operation. The features of the machine eliminate
errors in measuring, and it maintains its accuracy and requires
only slight attention for adjustment. As shown in Fig. 12,
it consists of a rigidly ribbed bed A on which two slides B and
C are mounted. Attached to the bed is a vernier scale D,

MEASiraiNG MACHINES 1 7

providing (or the approximate setting of slide C. Slide C
carries the tail measuring spindle / and a telescope for setting
the position of the slide. In addition, as shown in Fig. 13,
it carries an indicating spirit level E, which is one of the most
interesting features of the machine. When pressure is applied
to the measuring anvil through the piece being measured, this
spirit level is tilted out of the horizontal plane, due to the back-
ward movement of the anvil; the curvature of the vial gives a
movement to the bubble four thousand times the movement
of the anvil. This device is so sensitive that the slightest
expansion or contraction of the piece being measured, due to

varying temperatures, can be detected. The piece to be meas-
ured can be supported between the measuring points for any
length of time until all parts arrive at an even temperature.

The headstock or slide B carries the measuring wheel F,
which gives readings to o.ooooi inch, the graduations on the
measuring wheel being so arranged that the indicated size can
be read in decimals of an inch, the digits appearing in their
proper rotation. For example, as shown in Fig. 14, if the
size to be read is 0.31254, the first digit 3 is the highest figure
disclosed on the left-hand side of the scale carrying the vernier.
The second and third digits i and 2 are the highest main gradu-

i8 GAGING AND INSPECTION

atioa on the measuring wheel below the zero line on the vernier,
and the fourth digit 5 is the highest subdivision on the meas-
uring wheel below the zfero line on the vernier, while the fifth
digit 4 is that graduation on the vernier in line with any gradu-
ation on the measuring wheel.

The measuring spindle has a thread of the buttress form
cut especially deep to provide for wear, and has a range of

Fig. 14.

I inch. The threaded portion of the screw and nut is equal to
three times the length of range stated, so that the wear is even
and accuracy of pitch is maintained. An automatic adjust-
ment is also provided which maintains an even tension on the
measuring screw by keeping the effective faces of the screw
and nut in contact. It obviates backlash and facihtates accu-

MEASURING MACHINES

■ading. A knurled nut on the end of the spindle provides
for the rapid movement of the measuring screw. This is used
until sufficient pressure has been applied through the piece
being measured to bring the indicating bubble into motion,
For a sensitive movement, a line adjusting screw is provided
which is carried on an arm that can be clamped onto the meas-
uring wheel at any point by an eccentric. This screw, the
thrust of which is taken against the front horizontal bar, gives
the slow motion necessary. The front horizontal bar is also
used as a stop when it is desired to compare a number of parts
which have been made to accurate dimensions.

Owing to the great difficulty encountered in making the pitch
of a screw absolutely accurate for its entire length, a com-
pensator arrangement is provided. This consists of a second-
ary screw of the same pitch as the measuring screw, cut on
the rear end of the spindle. In contact with this screw is a
roller held in a lever C, Fig. 13, and mounted in such a manner
that any undulation on the crest of this thread imparts through
lever G a forward or backward movement to the vernier scale
H which is mounted on the vertical arm. In this way, any
inaccuracies in the pitch of the thread arc compensated for.

Operation of Newall Measuring Machine. — In setting this
machine, the first step is to ascertain the amount of free move-
ment in the anvil /. This is determined by bringing the head-
stock B and tailstock C together, so that the measuring points
come into contact, and then observing, by rotating the meas-
uring wheel F forward, the number of graduations passed in
mo\'ing the bubble of the spirit level indicator E from its
resting position. A small adjusting screw is provided under-
neath the rear end of the viai for returning the bubble to the
resting position. Assimiing that the free movement of this
vial is o.oi inch, the vertical arm carrying the scale // and the
vernier is swung around to a perpendicular position, or inclined
a little to the front of the machine, if more convenient for the
operator, and the measuring wheel set to read about o.oi inch.
Before doing this, however, it is necessary to sec that the meas-
uring faces of the screw and anvil are perfectly clean and that

GAGING AND INSPECTION

the headstock and tailstock are securely clamped to the bed.
Then the measuring screw is advanced until the indicator
bubble again reaches the measuring position and the reading
will be somewhere near zero. The vertical arm is then adjusted
so as to place the zero graduation on the vernier in direct line
with the zero graduation on the measuring wheel, and the
machine set at zero. It is advisable, however, to release the
measuring screw and advance it again to check this final setting,
when any slight inaccuracies may be corrected by a readjust-
ment of the vertical arm. The machine should be so set that
it is as free as possible from vibration and also from the effects
of frequent changes of temperature. It is essential that it
should not be exposed to the direct rays of the sun.

The foregoing description relates to the setting of the machine
for measuring pieces up to i inch. For measuring pieces over
1 inch and without the use of end-measuring rods for setting
the machine, the following method should be employed; The
tailstock C is moved along the bed to the left; then, through
microscope K, it is set to the nearest graduation, on the rule
on the bed, below the size to be measured, the headstock not
being moved, but left as previously set to the zero point. In
all cases of microscope settings, it is advisable to clamp the
tailstock slightly until, by means of the sensitive movement
obtained by the fine adjustment slide, the desired line on the
rule is perfectly central between and parallel to the two hair
lines in the microscope; then the tailstock can be firmly damped
in position. The part to be measured is held in supports be-
tween the measuring points, care being first taken to be sure
that all points of contact are perfectly clean. Then, by ad-
vancing the measuring screw in the same way as has previously
been described, until the bubble of the indicator assumes its
central position, the size of the piece b read off on the wheel
and vernier. When advancing the measuring screw, the
knurled nut on the end of the spindle is turned until sufhdent
pressure has been applied to start the bubble from its resting
position. Then the screw of the fine adjustment arm is turned,
moving the bubble slowly to its measuring position, which is

MEASURING MACHINES

the critical point in all operations of setting or measuring.
The subdivisions on the vial of the indicator are intended for
comparison only, but their approximate value may be deter-
mined by observation and calculation, if desired.

Should the alternative method — setting to end-measuring
rods — ^ be used, a rod of tlie nearest length to the size to be
measured is inserted between the measuring points and the
processes described in connection with setting to zero are re-
peated. The inaccuracy of such end-rods must be known, and
they should be regularly examined to detect any alterations
in length through wear or temperature changes. It is also
imperative that all surfaces and working parts of the machine
be kept clean and free from oxidization and dust. The lightest
possible oil should be used for lubrication, clock oil being
preferable, but if this cannot be obtained, paraffin oil should
be used on the measuring screw. The accepted mean tem-
perature at which verifications of standards are usually made
b 62 degrees F. This is the temperature at which this machine
is tested. The rules used on this machine are made in rec-
tangular sections from invar steel, which is noncorrosive and
only slightly susceptible to changes in temperature. This
machine will measure to 0.00000 1 inch, owing to the extreme
sensitiveness of the spirit-level indicator.

Liquid Indicator Measuring Machine. — A measuring ma-
chine that is used in the Laboratory of Technical Tests, Berlin,
Germany, and is considered to be accurate within 0.000004
inch, is shown in Fig. 15. The great precision of this machine
is obtained by connecting a movable plunger to a metal dia-
phragm, which acts upon a colored liquid. This diaphragm is
carefully fitted into a cylinder, and connected with the cylinder
is a graduated glass tube. The diaphragm is so sensitive that
even the exjjansion of the object being measured, caused by
touching it with the finger, is mdicated by the height of the
liquid. As far as possible, the temperature of the room is kept
at 68 degrees F., and a thermometer forms a necessary part
of the instrument. For gaging the work, an adjustable stand
is used which is raised to hold the work, if cylindrical, with

22 GAGING AND INSPECTION

its axis in perfect alignment with the measuring jaws of the
machine. The instrument, in addition, carries a graduated
wheel about to inches in diameter.

The chief use of this machine is to compare parts with
standards, and it is, therefore, not provided with a vernier
scale. The method of using it is as follows: The standard

test piece with which the parts are to be compared is brought
into contact with screw A and plunger B, being supported by
stand C. Graduated wheel D is then set with its zero mark
in line with the zero mark on arm E, and the height of the
hquid in tube F is noted. The standard is then removed and
the piece to be compared with it substituted. If the difference
between the two pieces is minute, the most accurate method
of determining it is by the height of the colored liquid. It is

MEASURINC MACHIOTIS

highly essential, in nuking accurate measurements, that the
pieces being measured be of the same temperature as the
machine, and hence tliey sliould be allowed to remain between
the measuring points until this condition is obtained.

Hartman Automatic Comparator. ^ The Hartman auto-
matic comparator which is used by the Internationa] Bureau
of Weights and Measures, France, is employed chieiiy for
comparing gages, and is not particularly adapted for originating
measurements. It was built to insure exactness in the size

id'

(..

^ ^ c=

L—

—

«=.»r»,r»

Fig.

HartmsD'i Automatic Compaiator

of gages of the same t>'pc which are made by different firms,
and is employed largely for testing gages used in gun manu-
facture. Referring to Fig. 16, which shows a diagram illus-
trating the principle upon which this machine is constructed,
it will be noticed that two end-measuring rods A and B are
being compared and are placed between the anvils C and D.
The anvil C is held stationary in the tailstock spindle E, and
the tailstock is free to slide along the base, which is graduated

' 24

GAGING AND INSPECTION

for a length of 1120 millimeters (44 inches). The anvil D can
be moved backward or forward in the head F by means of the
left-handed screw C, which has a pitch of 1 millimeter {0.039
inch). The rotation of this screw, instead of being noted on
a graduated sleeve, is measured by the position of the arms
H which pass in front of the graduated chart /. The length
of these arras is such that they describe a circle of 2 meters
(6j feet) in circumference, while the screw connected with the
head makes one revolution and travels a distance of i milli-
meter (0.039 inch). The multiplication of the movement of
the handles as compared with that of the screw is as one to two
thousand. By dividing a [wrtion of the circle on the chart
into one thousand parts of 2 millimeters each (0.078 inch),
when one of the arms has moved that distance — 2 millimeters
— the surface of the screw will have moved 0.000039 vnch.

In comparing the two end-measuring gages A and B, they
are placed automatically, one at a time, between the anvils C
and D, and their lengths registered on the chart / by the arms
which prick a hole as they pass. The difference between the
location of these marks gives exactly the difference between the
length of the rods. This instrument is entirely automatic in
its operation. The wheel carrying the arms is rotated by a
motor. The gages to be measured and supported are held in
carriers which operate automatically.

The Interferometer. — The interferometer is strictly a labo-
ratory measuring instrument, and while it is indispensable for
laboratory use, it is of little practical value to the average
manufacturing establishment. The interferometer is used for
measuring very small distances and angles in terms of wave
lengths of light. It furnishes the most accurate known method
for testing the uniformity of a screw or the perfection of a
straightedge, making use of the phenomenon known as the
"interference" of light. Light travels in waves, and a simple
illustration of this is to compare a light wave to a rope which is
fastened at one end and moved up and down rapidly at the other.
In the movement of the rope, the distance from the highest part
of one wave to the highest part of the next would be a wave

MEASURING MACHINES

length, and. the distance which the rope moves up or down from
its middle position would be called its "amplitude." In the case
of light vibrations, the amplitude determines the intensity of
the light and the wave length determines the color. For ex-
ample, light waves which are about 0.00003 inch long appear
to the eye as red. The wave length of yellow light is about
0.000023 inch; of blue light, 0.000018 inch, etc. Two pieces
of plate glass held in contact may be used to demonstrate the
interference of light. If held at an angle to the light, color

Tig, 17. Diagram illustrating Principle of Interferometer

bands will be noticed in circles and odd shapes throughout
the plane of the two surfaces in contact. These colors indi-
cate measurable variations in the surfaces from a true plane.

Principle of the Interferometer. — The Michelson interfer-
ometer, which is employed for precise laboratory measurements
in the Bureau of Standards, is shown diagrammatically in
Fig. 17. Artificial light is used with this instrument to pro-
duce the different light waves which indicate the variations
from truth of the planes or other parts being measured. Sodium

UEASURING MACHINES

ror E have to pass three times through plate C before reaching
telescope F. A compensator plate G is, therefore, put in the
path of the other rays, so that the light reflected by D has to
pass twice through G and once through C before it reaches the
telescope. Plates C and G arc cut from the same piece of glass
so that they are of the same thickness, the original piece of
glass having been ground and polished until its surface is plane
and parallel to within from 0.000002 to 0.000005 inch, accord-
ing to the accuracy of the measurements to be made.

When the paths of light from C to D and from C to £ have
been fixed nearly equal, the mirrors are so adjusted that the
color fringes will appear as either horizontal or vertical lines.
Then as one of the mirrors is displaced, the color bands pass
in succession before the eye of the observer, who can count them
as they pass the reference point — the crosshairs in the telescope.

Construction of the Interferometer. — The interferometer is
constructed in different forms, depending upon the class of
work (or which it is to be used. For instance, an interferometer
which would be used for checking the accuracy of angles would
be constructed on a different principle from that used for test-
ing the accuracy of straightedges or screw threads. For test-
ing the accuracy of a screw thread, the interferometer would
have a form somewhat like that shown in Fig. 18. The screw
S to be tested is mounted in the bed T and is used to move the
carriage U carrying the mirror E. The mirrors are adjusted
so that the fringes appear in circles. This will happen when
the fixed and movable mirrors D and E, respectively, are equi-
distant from plate C which divides the light, and when the
reflection from mirror E in plate C is exactly parallel to the
face of movable mirrjr E. The variation in the pitch of the
screw is determined by the number of fringes that pass through
mirror C. Tf the number of fringes is the same for each turn
or fractional part of a turn of the screw, the screw is accurate;
but if the number varies, the screw is inaccurate, the amount
of the inaccuracy depending upon the difference in the number
of fringes. By this method, inaccuracies are detected in a

V that a

s small

as 0.0000005

inch.

CHAPTER II
LIMITS AND TOLERANCES

Previous to the adoption of gages and inspection fixtures,
the component parts of mechanisms were made by fitting one
to another. As an illustration, take a gasoline engine and
assume that the cylinders were finished by reaming. The
pistons would be made approximately to size by caliper meas-
urements and then fitted to the bore of the cylinders, the
cylinders acting as a gage. In this way, of course, interchange-
ability is difficult, if not impossible. The question of having
each part alike within given limits, however, has not always
been considered practicable or necessary, and the first appli-
cation of the interchangeable system was adopted in the pro-
duction of rifles. In the past few years, the subject of gaging
and inspection methods has received considerable attention.
This has been due as much to the desire to reduce manufac-
turing costs as to the necessity for having all parts inter-
changeable.

It has been clearly demonstrated in plants where the inter-
changeable system has been properly applied that a less skilled
grade of mechanics can be employed and still turn out inter*-
changeable parts. It requires the services of a first-class
mechanic to make a number of parts exactly alike, without
a gaging system, but a second-rate mechanic can make a large
number of parts exactly the same — within the required limits
— and much cheaper, with a proper gaging and inspection
system. Hence, the advantage gained by interchangeable
manufacture is not only that all parts are made alike, but that
the production costs are greatly reduced at the same time.

In the present chapter, the fundamental principles governing
the setting of limits and tolerances for various classes of work

will be dealt with in detail.

LIMITS AND TOLERANCES 29

Development of Interchangeable Manufacture. — The origi-
nal idea of making parts interchangeable must be credited to
Le Blanc, a French mechanic, who about 1785 made rifle parts
on an interchangeable basis, but the first practical application
of the principle on a large scale is due to Eli Whitney, a manu-
facturer of Whitneyville, Conn., a small town just outside
New Haven. Mr. Whitney first applied this principle to the
production of firearms for the United States Government, with
the object of being able to replace broken parts of firearms
with new ones when in the field. In 1798, Mr. Whitney was
given a contract for firearms which were produced on the inter-
changeable basis. The lock of these firearms was made by
employing hardened templets to which the parts were accu-
rately filed. About the same time Simeon North adopted the
principle of interchangeable manufacture in the production of
army pistols, and from the year 1800 great strides were made
in this direction. The first complete system of interchangeable
manufacture is credited to Elisha K. Root, a New England
mechanic, who made a complete system of jigs, fixtures, tools,
and gages for use in the Colt Armory at Hartford.

The Limit System. — The limit system which forms the basis
of interchangeable manufacture is applied in a variety of ways
in various manufacturing plants. In some cases, the limit
system, as generally understood, is not applied in its entirety.
For instance, parts^ which must fit together are made with cer-
tain allowances, but no tolerances are given to take care of
imavoidable errors in the manufacture of parts. This cannot
be called a limit system, because no limits are given. Conse-
quently, a great deal more time and money is spent in making
the parts than would be the case if the complete system were
adopted. In cases where the limit system is not adopted, the
parts are made to direct measurement, using standard meas-
uring tools, and unless great care is taken and experienced
workmen employed, considerable fitting and assembling is
necessary. With a complete system of gaging and inspection,
this fitting and assembling is almost, if not entirely, done away
with, and manufacturing costs are thereby greatly reduced.

3°

GAGING AND INSPECTION

The advantages of the limit system are not always thoroughly
appreciated, and in the following an endeavor will be made to
explain some of the chief reasons why this system should be
adopted where it is desired to produce parts cheaply as well
as interchangeably.

Advantages of the Limit System. — The adoption of a limit
system and the practice of working to limit gages has many
advantages. In the first place, it makes an interchangeable
product possible and eliminates the necessity of depending
upon the judgment of the workman; and probably what is of
still more unportance, it reduces the amount of spoiled work
to a minimum. The initial cost required to install the system
in some cases b heavy, but when it is considered that a properly
organized limit system greatly reduces inspection and manu-
facturing costs, the advantages to be gained will, generally,
more than offset the cost involved. In adopting a limit system
for ordinary work, it is necessary to take cither the hole or the
shaft as a standard. When holes are finished by grinding, it
makes little difference which is decided upon. When the hole
in the work is finished by reaming or similar tools, and can be
duplicated in size with reasonable commercial accuracy, it is
advisable to adopt the size of the hole as a standard. There
are, of course, exceptions to all rules, and in some cases manu-
facturers using cold-roUed steel shafting lind that it is preferable
to use the shaft as a basis instead of the hole. As a general
rule, however, the hole basis should be adopted-
Limit, Allowance, and Tolerance. — The expression "limit"
as employed in machine shop work refers to the permissible
tolerance in machine work. A shaft, for example, is required
to be one inch in diameter; but it is generally urmecessary,
in commercial work, to finish the shaft to a diameter of exactly
one inch. It is, therefore, common practice to specify the
"limit" — that is, the deviation from the true or nominal size
which b permissible. The limit is generally stated by giving
the amount that the dimension may be larger or smaller than
the nominal size. The diameter of the shaft, for example,
may be given as "one inch plus or minus o.ooi inch," which

LIMITS AND TOLERANCES , 3 1

means that the shaft will pass mspection if it is not more than
o.ooi inch larger or o.ooi inch smaller than one inch. A
common method of expressing this briefly on a drawing is to
state the diameter as "i ±0.001/' Another method is to

give the dimension as " \ ^'999 f »»
^ \ i.ooi J

There are a nmnber of terms closely allied to the term "limit"
used in the machine shop. Among these are ** tolerance/'
"working tolerance/' "permissible tolerance/' "necessary tol-
erance/' "clearance/' "working clearance/' "allowance/'
/'working allowance/' and "finish." Of these terms, all those
containing the word "tolerance" signify the difference between
the majdmmn and minimum limits; the terms containing the
word "clearance" are equivalent to those containing the term
"aUow^ince"; and the term "finish" implies the final touch
or elaboration that is given to the work, irrespective of the
accuracy of the dimensions required. Therefore, as regards
the dimensions, there are only three expressions necessary —
"limit," "tolerance," and "allowance." The meaning of
"limit" has been explained. "Tolerance" is the total differ-
ence between the maximum and minimum dimensions of the
work. "Allowance," often termed "clearance," signifies the
difference between the working parts to produce a certain fit
and to provide for lubrication. The amount of the allowance
depends upon the class of fit required, whether a running fit,
sliding fit, push fit, drive fit, etc. The practice of making
drawings which specify the exact amouht of allowance between
different parts, as well as the limit, is TNecommended. When
this practice is followed, there can be no controversy when
work is inspected, because everything is plainly stated on the
drawing, and there is no opportunity for misunderstanding as
to the accuracy required. The expression "a limit of o.ooi
inch" should never be used, as it is indefinite, giving no idea of
whether this limit is above or below standard size. It may
mean either o.ooi inch above; o.ooi inch below; or possibly
0.0005 above and below standard size. When the limit is
expressed as ±0.001 or ±0.0005 inch, there can be no mistake.

(lACJlNG AND INSPECTION

( i

', '

If "

1
(

k-e;".?"'

r. —

.-.—__

-~'~

i^ ..

)

: t;

— -

■ '

• i'l ""'

LIMITS AND TOLERANCES 33

To illustrate the expressions defined in the preceding para-
graphs, suppose it is necessary to make a shaft with a good
running fit in a bushing, as illustrated in an exaggerated form
by the three detailed views in Fig. i. The difference between
the nominal diameters of the shaft and hole is 0.002 inch, which
is known as the allowance. The limits on the diameter of the
hole are —0.00025 inch and +0.0005 inch, and on the shaft,
±0.00075 inch, so that ''the tolerance on the hole is 0.00075
inch, and on the shaft,' 0.0015 inch. For a nominal hole of
I inch and a shaft of 0.998 inch, this gives a maximum hole
of 1.0005 inch and a minimum shaft of 0.99725 inch — a differ-
ence of 0.00325 inch; and a minimum hole of 0.99975 inch
and a maximum shaft of 0.99875 inch, a difference of o.ooi inch.
From this it will be seen that the "set'' allowance between the
shaft and the hole is what is desired, but seldom obtained.

Setting Manufacturing Limits on Interchangeable Parts. —
The setting of limits on work which must be made inter-
changeable is of vital importance. It is a subject which, gen-
erally, does not receive the consideration that it deserves. Many
manufacturers set the limits much closer than is necessary
to obtain interchangeability. When a part does not fieed to
be made to more accurate limits than ±0.003 inch, this limit
should be tolerated. Where greater accuracy is necessary, the
limits should be closer.

The practice of specifying limits saves much needless expense.
For instance, many manufacturers specify the length of a
shaft in fractions of an inch and do not give any limits, with
the result that the toolmaker or mechanic endeavors to bring
the parts exactly to the size mentioned. This is a short-sighted
policy, especially where 5 ^ inch more or less than the size given
on the drawings would make no practical difference in the
efficiency of the machine. Take also, for instance, gages, jigs,
fixtures or other special tools used in the production of inter-
changeable parts. It is the practice of some concerns not to
give any manufacturing limits on these tools, specifying that
all dimensions should be exact. Hence, much time is consumed
in making the tools, which even under the most favorable con-

GAGING AND INSPECTION

ditions cannot be made exactly alike. Some go so far as to
state that a plug or ring gage should be made exact, and have
no limit of error at all; but this is impracticable, as it is almost
impossible to make two parts exactly alike; a slight change
in temperature will easily change a plug gage diameter 0.000025
inch. Several large manufacturing concerns have set limits on
work produced in the tool-room with satisfactory results.

Methods of Establishing a System of Limits. — Many meth-
ods have been evolved for establishing a system of limits, and
careful study of this subject has revealed the fact that prac-
tically no two manufacturers use the same system of setting
limits, or give the same permissible amount of error in manu-
facturing. In some cases, the limits are stated directly on
the drawing; in others, the size of the part is given either in
fractions or in decimals of an inch, the method of giving
the dimension being an indication of the permissible linut
allowed. In some cases it is stated on the drawing that, where
dimensions are given in fractions of an inch, a tolerance of
^i inch above or below the dimension given is permissible.
If the dimensions are given to two decimal places, the limit
can be ±0.005 inch; to three decimal places, ±0.0015 inch;
to four decimal places, ±0.0005 inch; and to five decimal
places, ±0.0002 inch.

It is a difficult matter to decide upon the i)ermissible error,
as this depends entirely ujjon the character of the work and
the conditions under which the parts are to operate. For
instance, there are different classes of fits desired, such as push,
drive, running, slide, force, etc. The variation or allowance
between the female and male members depends upon several
factors, among which might be mentioned; Diameter and
length of hole, materia!, speed, load carried, etc. Conse-
quently, no set rules can be established for this work. Sev-
eral concerns, however, have established limits derived from
practice, which, with proper judgment, can be used to good
advantage. One system which has Iwen , adopted by the
Newall Engineering Co. (England) is given in Tables I to V,
inclusive.

LIMITS AND TOLERANCES

There are several questions to be decided in setting limits
on parts which must fit together. Ignoring, for the present,
the method used in making the parts, which is an important
matter, the two points which should be settled are, first, per-
missible maximum and minimum allowances between the shaft
and hole; and second, manufacturing limits or tolerance for
the hole. When these two points have been satisfactorily
decided upon, it is a simple matter to establish limits on both
the hole and the shaft. As an illustration, assume that it is
necessary to obtain a nmning fit between the shaft and bushing
shown in Fig. 2, and that the hole in the bushing is to be pro-
duced by reaming. The first question to decide is the maxi-
mum and minimum allowances. In this particular case, say

._i_

0.998

-H).0006*
-«.0O06'

BUSHINQ

SHAFT
B

Machinery

Fig. 2, Diagram iUustratiiig Method of setting Limits for Obtaining

Running Fit

that the maximum allowance is 0.003 '^^^ ^md the minimum,
0.001 inch. The next question to decide is the permissible
tolerance for the hole. As a standard reamer cuts slightly
oversize, but, on the other hand, as the reamer may be slightly
worn, make the hole as shown in Fig. 2, i.ooo inch ±0.0005
inch. This gives a tolerance in the hole of o.ooi inch. Now,
to set the limits for the shaft, subtract from the nominal diam-
eter of the hole, or i.ooo inch, the mean allowance, or 0.002
inch. This gives a nominal shaft diameter of 0.998 inch. The
limits can now be set for the shaft in a similar manner to that
used for the hole, thus giving a manufacturing tolerance of
0.001 inch* Checking back to prove that the figures are cor-
rect, it is found that the largest hole is 1.0005 i^ch and the
smallest shaft, 0.9975 inch, which gives an allowance between

GAGING AND INSPECTION

these two sizes of o.cx)3 inch — the maximum permissible
allowance. The minimum size of hole is 0.9995 inch and the
maximum shaft, 0.9985 inch, which gives a difference of o.ooi
inch, or the minimum allowance between the hole and the
shaft. The manufacturing limits set on the work do not affect
the original established allowances between the parts, when
the method outlined above is followed, and there is no danger

Table I. Tolerances for Standard Holes

■ (Newall Engineering Co.)

Class

Nominal
Diameters, Inches

o-^i

9i«-i

iH«-2

2H«-3

3H6-4

Max. Limit
Min. Limit
Tolerance

+0.00025

—0.00025

0.00050

4-0.00050

—0.00025

0.00075

4-0.00075
—0.00025

O.OOIOO

4-0.00100

—0.00050

0.00150

4-0.00100

—0.00050

0.00150

Max. Limit
Min. Limit
Tolerance

4-0.00050
—0.00050

O.OOIOO

4-0.00075

—0.0005c

0.00125

4-O.OOIOO

—0.00050
0.00150

4-0.00125

-0.00075
0.00200

4-0.00150

—0.0007s

0.00225

Class

Nominal
Diameters, Inches

4^in-.S

5'i«-6

6)18-7

7^i«-«

8h6-9

Max. Limit
Min. Limit
Tolerance

4-0,00100-1-0.00150

— 0.00050 —0.00050

0.00150 0.00200

4-0.00150

-0.00075

'0.00225

4-0.00175

— 0.00075
0.00250

4-0.00175

— O.OOIOO

0.00275

Max. Limit
Min. Limit
Tolerance

4-O.OOI75

-0.00075

0.00250

4-0.00200
— O.OOIOO

0.00300

4-0. 00225I 4-0. 00225
—0.00100—0.00125

0.00325; 0.00350

4-0.00250

—0.00125

o.oo3f5

Tolerance is provided for holes, which ordinary standard reamers can produce, in two grades.
Classes A and B, the selection of which is a question for the user's decision and dependent upon
the quality of the work required; some prefer to use Class A as working limits and Class B as
inspection limits.

of having the minimum hole the same size as the maximum
shaft, which is sometimes the case when the manufacturing
limits are set in a haphazard manner.

Allowances for Various Classes of Fits. — In order to provide
for various classes of fits, such as push, drive, force, etc., it is
necessary to make certain allowances between the diameters
of the hole and the shaft. As the hole basis is taken to be
the standard in most cases, the size of the hole, therefore, is
the first question to decide. Table I gives two lists of toler-
ances for standard holes varying from o to 9 inches in diameter

LIMITS AND TOLERANCES

Table U. Tolerances for Running Fits
(Newall Engineering Co.)

Class

Nominal
Diameters, Inches

0-\2

9i6-i

iHa-a

3H«-3

3H«-4

Min. Limit
Max. Limit
Tolerance

— 0.0020C

—O.OOIOO

O.OOIOO

—0.00275

—0.00125

0.00150

-0.00350

-0.00175

0.00175

—0.00425

—0.00200

0.00225

—0.00500

—0.0025c

0.00250

Min. Limit
Max. Limit
Tolerance

—0.00125

—0.00075

0.00050

—0.00200

— O.OOIOC
O.OOIOO

—0.00250

—0.00125

0.00125

—0.00300

—0.00150

0.00150

—0.00350

—0.00200

0.00150

Min. Limit
Max. Limit
Tolerance

-0.00075

—0.0005c

0.00025

—0.00125
-0.00075

0.00050

—0.00150

-0.00075
0.00075

—0.00200

— O.OOIOO
O.OOIOO

—0.00225

— O.OOIOO

0.00125

Class

Nominal
Diameters. Inches

4H6-S

5! la-^

6h'«-7

7M6-8

8h'«-9

Min. Limit
Max. Limit
Tolerance

-0.00575

— 0.0030c

0.00275

—0.0065c

-0.0035c

0.00300

—0.00675

-0.0035c
0.00325

—0.00700

-0.00350
0.00350

—0.00750

-0.00375
0.00375

Min. Limit
Max. Limit
Tolerance

—0,00400
—0.00225

0.00175

—0.0045c

—0.00250

0.00200

-0.00475
—0.00275

0.00200

—0.00500

-0.00275

0.00225

-0.00550

—0.00300

0.00250

Min. Limit
Max. Limit
Tolerance

—0.00250

—0.00125

0.00125

—0.00275

— 0.00125

0.00150

— 0.00275

— 0.00125
0.00150

—0,00300

—0.00150

0.00150

—0.00300

—0.00150

0.00150

Running fits, which are the most commonly required, are divided into three grades: Class
R. (or engine and other work where easy fits arc wanted; Class S, (or high speeds and good
average machine work; Class T, (or fine tool work.

Table UL Tolerances for Push Fits

(Newall Engineering Co.)

Nominal
Diameters, Inches

o-^'i

»i«-I

lh'6-2

2M6-3

3MS-4

Min. Limit
Max. Limit
Tolerance

-0.00075

—0.00025

0.00050

—0.00075

—0.00025

0.00050

-0.00075

—0.00025

0.00050

— O.OOIO

—0.0005
0.0005

— O.OOIO

—0.0005
0.0005

Nonunal
Diameters. Inches

4H«-S

sH«-6

6iifl-7

7M«-8

8H6-9

Min. Limit
Max. Limit
Tolerance

— O.OOIO

-0.0005
0.0005

— O.OOIO

—0.0005
0.0005

— 0.00125

— 0.00050
0.00075

— 0.00150

— 0.00050
O.OOIOO

—0.00150
—0.00050

O.OOIOO

38 GAGING AND INSPECTION

and known as "Classes Aand B." Class A is preferred by some
manufacturers as manufacturing limits, and Class B as inspec-
tion limits. In using the hole as a basis or standard, the shaft
is made to suit the hole, depending upon the type of fit desired.
The classes of fits used in ordinary practice are as follows:
Running, push, drive, and force fits.

Running Fit. — Running fits, as specified in Table II, are
divided into three classes or grades, known as "Classes R, S,
and T." Class R is used principally for engine and other
work where easy fits are required, and also for shafts running
in several bearings or for a single bearing of unusual length.
Class S is used for high speeds and good average machine work,

Table IV.

Tolerances for Driving FiU

Willi Engineering Co.)

DmmttH.. Incha

»i.-i

xH.-.

«H.-3

......

Max. Limit
Min. Limit
Tolerance

+o .00050
0.Q0025

+0.00100

+0.0007S

0.00015

+0.00.50
+0.00100

0.00050

+0.00250

+0.001SO

+0,00300
+0-00200

Nominal
Diameten, liKhH

<H>-5

iii.-«

6;(.-j

8(U-9

Max. Limit
Min. Limit
Tolerance

+0,00350

+0.00400
+0.00300

+0.00450

+0.00300

o.ootso

+0,00500

+O.OOJSO

0,00150

+0,00550

+0,00400

0,00150

and also for shafts running in a single bearing of ordinary
length. Class T is for fine tool work, sliding shafts, and similar
work. The limits given in Table II for running fits can also
be employed for other than revolving fits where it may be
advisable or necessary to limit the manufacturing error on the
parts.

Push Fit, — Push fits, the limits for which are given in Table
III, are for shafts that are forced into a hole by hand and that
would be free to rotate without seizing, but not free enough
to rotate under anything but a very slow speed. Usually there
is sufficient friction between the hole and the shaft to prevent
free rotation. Push fits arc usually employed where one mem-

LIMITS AND TOLERANCES

ber is fitted into another and then held in place with a key
or pin.

Drive FU. — Drive fits, Table IV, are used for shafts that
are to be driven into holes either with a heavy hammer or with
a light arbor press, and are distinguished from push fits in that
shafts made with a drive fit can be easily driven into a hole,
but will not be able to rotate.

Force FU. 7- Force fits. Table V, are used for shafts which
require either hydraulic pressure to force them into the holes,
or for those in which the hole is expanded by heating for shrink-
ing onto the shaft.

Table V. Tolerances for Force Fits

(Newall Engineering Co.)

Nominal
Diameters. Inches

o-H

h*-i

lH«-2

2H«-3

3M6-4

Max. Limit
Min. Limit
Tolerance

+0.00100

-|-o. 00050

0.00050

+0.00200

+0.00150

0.00050

+0.00400
+0.00300

O.OOIOO

•

+0.00600

+0.00450

0.00150

+0.00800

+0.00600

0.00200

Nominal
Diameters. Inches

4H«-5

sH«-6

6^(6-7

7H«-8

8H«-9

Max. Limit
Min. Limit
Tolerance

+0.01000

4-0. 00800

0.00200

+0.01200

+0.01000

0.00200

+0.01400

+0.01200

0.00200

+0.01600

+0.01400

0.00200

+0.01800

+0.01600

0.00200

Establishing Allowances and Tolerances for Various Classes
of Fits. — The method used in establishing allowances and
tolerances for a running fit has been described in a general
way. Taking a concrete example, illustrated at ^4 in Fig. 3,
and using the limits of tolerance given in Tables I and II,
assume the nominal hole to be i.ooo inch in diameter and use

Class A limits. The hole here would be i .000 \ "^ ^^^^So f jj^^j^

( — 0.00025 )

This gives a manufacturing tolerance of 0.00075 i^ch- The

diameter of the shaft is then made smaller than the hole by

making use of the limits given in Table II. Reference to this

table will show that the shaft is made < ""^oo^^s j ^^^ ^^^ ^j^^

I -0.00275

GAGING AND INSPECTION

the nominal hole. This gives a hole and shaft of the following
dimensions: Maximum hole, 1.0005 inch; minimum, 0.99975
inch; maximum shaft, 0.99875 inch; minimum, 0.99725 inch.

^4-0. mw;;

..ife* 1

i 1^

HOL,

''>'^

'«i'-S:S-

^ 1

T^ !)

PUiM Fl

o«i'13-=-

'^fVSS- 1

^ t

„T

DHIVINQ

— 1

.»iL=L

- —

^^'" ■'

*c-o«(ncT»

The difference or allowance between the minimum hole and
maximum shaft is o.ooi inch, and the difference between the
maximum hole and minimum shaft, 0.00335 inch. The tol-

LIMITS AND TOLERANCES 41

erance between the maxiinum and minimum hole is o.cxx)75
inch, and the tolerance between the maximum and minimum
shaft, 0.0015 inch.

In making a shaft which must be a push fit in a hole, the
amount of tolerance for the shaft is considerably less than for
an ordinary running fit. As indicated at 5 in Fig. 3, the
tolerance for the shaft is made with a minimum limit of —0.00025
inch and a maximum limit of —0.00075 inch. This allows no
theoretical difference between the maximum shaft and minimum
hole; in other words, the smallest hole and the largest shaft
are of the same dimensions, or 0.99975 inch in diameter. The
difference between the largest hole and the smallest shaft is
0.00125 inch.

In making a drive fit, it is necessary to have the shaft slightly
larger than the hole, so that the required amount of grip on
the shaft will be obtained. As before, the hole is made with
plus and minus limits, as shown at C in Fig. 3. The shaft is
made larger than the hole and has a maximum limit of +Q.001
inch and a minimum limit of +0.00075 ^^^^' This produces a
condition in which the largest hole is 0.0005 ^^^ smaller than
the largest shaft, and the smallest hole is 0.00125 inch smaller
than the largest shaft. This insures in all cases that the parts
will go together with a suitable driving pressure.

The conditions for a force fit are similar to those for a driving
fit, with the exception that a greater allowance is made between
the diameters of the shaft and the hole, in order to obtain a
tighter union between the parts. As shown at D in Fig. 3,

the shaft is made i.ooo \ | ^-^^^^ ( inch. This gives an allow-

\ +0.0015 ) ^

ance between the smallest hole and largest shaft of 0.00225
inch, and a difference between the largest hole and smallest shaft
of o.ooi inch.

Methods of giving Limits on Drawings. — In setting manu-
facturing limits on interchangeable parts, various methods are
adopted for expressing the limits of error to be tolerated.
Expressions such as plus and minus, Tow and high, maximum
and minimum are commonly used. There are two important

' 42

GAGraC AND INSPECrrON

points to be observed when setting manufacturing limits :
First, to so set these limits that the operator can clearly under-
stand the drawing. Second, to express them in such a way
that the draftsman who checks the drawing can conveniently
tell whether the parts have been properly dimensioned or not.

A practical example, which will serve to illustrate this point,
is shown in Fig. 4. Here a set of gears for the lower part of

— 1 f^--^^.i,Bi!;IK!;

an automobile transmission is shown in section; shaft a is shown
supported in two fixed bearings. The four gears b, c, d, and e
are keyed to this shaft and separated by a spacing washer.
The washer provides for inaccuracies of the parts, and while
this practice is not recommended, the example is so simple
that it has been used in place of a more complicated one.
In Fig. 4, two methods are used for dimensioning the parts.

LIMITS AND TOLERANCES 43

As shown at A, the minimum and maximum sizes or widths
of the gear shoulders are given and the minimum and maxi-
mum distances between the bearings. In giving the dimensions
in this manner, it makes it extremely difficult for the checker
to determine whether or not any mistakes have been made in
dimensioning. It requires a careful addition of the different
dimensions to find if the required allowance between all the
gear shoulders and bearing faces has been provided. Assuming
that the minimum allowance between all the gears and bear-
ing faces is 0.00a inch and the maximum allowance, 0.005 inch,
the method of setting the limits on the drawing would be as
follows :

Inspection will show that there are five parts, so that the
total manufacturing limits on the gears should not exceed
0.0025 inch, as a limit also must be provided for the distance
between the bearing faces. In other words, there are six di-
mensions to take into consideration, allowing a limit of 0.0005
inch on each; this totals 0.003 inch, or the difference between
the maximum and minimum allowances. As soon as this
question is settled, it is a simple matter to place the limits on
the different parts. For the gears, no plus limits are tolerated
and a minus limit on each part of 0.0005 'nch is provided. The
dimension given on the drawing to represent the distance be-
tween the bearing faces is a nominal dimension and is equal
to the sum of the gear shoulders and washer. But as a mini-
mum allowance of 0.002 mch is necessary, the minimum dis-
tance between the bearing faces would be the nominal dimen-
sion, or 4.625 inches -f- 0.002 inch, and the maximum, -4.625
inches -\- 0.0025 inch. To show that this is correct, add the
nominal dimensions on the gears and washer, which equals
4.625 inches, as the maximum. The minimum is 4.625 inches
— 0.0035 i"<^i or 4.6225 inches. The maximum distance be-
tween the bearing faces is 4.6275 inches, and the minimum,
4.6270 inches. This gives an allowance between the minimum
gear shoulders and maximum bearings of 0.005 inch- and an
allowance between the maximum gear shoulders and minimum
bearing faces of 0.002 inch.

44 GAGING AND INSPECTION

Inspection of the two methods of giving these dimensions
at A and B will show that the one illustrated at B is the
simpler from the standpoint of checking the drawing. At B,
no plus limit is allowed for the gears and no minus limit for
the space between the bearings; hence, the checker can imme-
tliately see that these gears are to be made with a running fit
between the bearing faces. In the case shown at A, this is
more difficult to ascertain without actually checking up the
different dimensions and ascertaining the allowance between
the gear shoulders and bearing surfaces.

Limit System for General Work. ^ The system of Umits
described in the following paragraphs was devised for use in
an engineering office which specializes on general machine
design. The various machines designed are built in different

CAGE LIMITS.

All holes are stand

rd reamer size ufiless

noted.

+ A Indicates (rom

pluQ size to .001 over

-A same under,

+ B Indicates fror.

.001 to .002 over size

-B same under.

+ C indicates from

.003 to .005 over size

— C same under,

Finish dimensions

nmarkod, ffom ,005 u

der to .006 over.

Fig. ;. Form o( Gaee Limit Sjstem (or General Work

factories, depending upon the client for whom the work is done,
and often without supervision by the engineer; so it is evident
that any system of limits used must be simple and readily
understood. The method to be descriljed also avoids the work
required in placing the limit sizes on the drawing. This, of
itself, is something of an item on any design requiring a con-
siderable number of details. E.xperience, therefore, led to a
tentative method that has been developed into a system, ui
no sense perfect, but one which can be readily used in general
work, and which msures good work without fitting or questions
as to fits; these are decided by. the designer and indicated in
a way that is easily understood by the workman. This result
is accomplished by affixing, to all dimensions which require
limiting, a plus or minus sign and a letter. A, B, or C, which

LIMITS AND TOLERANCES

indicates the amount of variation; plus indicating over nominal
size and minus indicating under size. A rubber stamp giving
the data presented in Fig. 5 is used on each detail sheet and
the various details arc marked accordingly.

The gist of the method is this: If a dimension has a plus
letter after it, it must be to size or over, within the limits called
for by the letter. Similarly, U a dimen-sion is followed by a
minus sign, it cannot be oversize and may be under, according
to the letter. A dimension without a plus or minus letter
indicates that the size is nominal, and ordinarily careful work
is all that is required. Slots and depressions that would be
measured by a plug gage may be considered as holes, and come
under the heading "all holes are standard reamer size unless

Fig. 6. EzamplBB of Delails showing Ubs of Gage Limit SyBtem

noted." Working on this basis, studs, shafts, slides, etc., are
marked minus if a running lit, plus, if a driving or press fit,
and the limiting letter according to the judgment of the designer.
Both the plus A and the minus A dimension may ordinarily
be considered as plug size, it being noted that the plus sign
would be used where it was essential that the part be abso-
lutely rigid, as in the neck of a stud where it fastens or is
screwed into another part, making it integral; the minus sign
would be used where a part is subject to frequent removal,
as in a stop plug or other part where ease in removing is essen-
tial. Drilled holes may be dimensioned in thousandths of an
inch, and cored holes should be specified. Fig. 6 will illustrate
the application of this method to detail work. The roller
shown is a running fit on the stud, and it is evident that the
two details may be made independently and yet work together

GAGING AND IN3FE(

Ivithout subsequent fitting. Limits are given, both on the
f length of the shoulder on the stud and on the width of the
[ roller and this apparently departs from the general method
described. It seems advisable, however, to allow variation
when possible rather than absolute sizes, and in such cases
as this, side clearance may be split up between the two parts
with satisfactory results.

Under certain conditions, the limits shown in Fig. s cannot
be used without modification. One machine, for example, may
be of a character that prevents a maximum variation of more

CAGE LIMITS.

All tioloB are standard reamer size unless

noted.

+ A indicates from plug size to .0005 ov

r,-A la

me under.

+ B indle-tes from X005 to .001 oversiz

B,-B sa

me under,

-1-C Indicates from .001 to .002 over size

-Csa

me under,

ndor to

003 over.

CAGE LIMITS.

All holes are standard reamer a.ie unless

noted.

+ A irrdleales from plug size to .005 ove

-A sa

Tte under.

+ B indicates from .005 to .010 over size

-Bs.

me under,

+ C Indicates from .010 to .015 over size

-Csa

me under.

Finish dimensions unmarked, from .015 u

nder to

015 over.

Fig. 7. Special Forms of Gage Limit Sjstem lor Fine and Rough
Work

than 0.002 inch; another may be of an exactly opposite char-
acter, in which a maximum variation of 0,015 inch or even
more is allowable, without affecting the action. To meet these
conditions, another rubber stamp may be used, and the values
of the limiting letters changed, as shown in Fig. 7.

After a year or more, it has been found that little or no
explanation is required when a drawing marked as described
is put into the shop; moreover, the men seem to take kindly -
to it. In estimating costs, it is found valuable as an aid to
the contractor in getting a closer figure than would be ob-
tmnable where nicety of finish would be a matter of guess work.

^■^

CHAPTER III
REFERENCE, WORKING, AND INSPECTION GAGES

A SATISFACTORY gaging system should be built around
the basic reference and limit snap and plug gages. Reference
gages are divided into three classes, as follows: Working gages
for shop use; inspection gages for final checking; and gages
used in testing and adjusting both working and inspection gages.
Limit gages include two classes; namely, allowance and tolerance
gages. Tolerance gages provide for reasonable error in workman-
ship, whereas allowance gages take care of the necessary differ-
ence in the sizes of two pieces which fit together; in this classi-
fication, the female and male gages are referred to collectively
and not individually.

Reference Gages. — In addition to the reference blocks and
rods shown in Figs, i and 2, Chapter I, reference gages are made
in several other forms, the most common or conventional type
being the standard plug and ring gage shown in Fig. i of this
chapter. This type of gage is of little or no value in connection
with interchangeable manufacture, as it is made to one standard
size and can only be used for setting micrometers, calipers, and
other measuring instruments. Owing to the great accuracy of
this gage, it should not be used as a working gage. Plug gages
are made to standard size within very close limits, and most
manufacturers guarantee them to be within o.oooi inch of
standard size, although as a matter of fact they are often made
considerably more accurate than this. The tolerance is over
rather than under the standard, so as to provide for wear. The
ring gage is then made to fit the plug and is not measured.
Theoretically speaking, there is no difference between the diam- -
eter of the plug and the diameter of the hole in the ring, and they
are put together only with great difficulty by an experienced
gage-maker. It is done by coating the plug and the ring with a

film of light oil, placing them in alignment, and with a quick
twist inserting the plug in the ring. The plug, however, must be
kept in motion to prevent it from "freezing." If the ring and
plug are aUowed to remain stationary, relative to each other,
they will stick to each other in a short space of time, and can
only be separated by force. One way of separating them is to
hit the ring quickly on the bench, and immediately pull out the
plug, using a twisting action. This, however, also requires con-
siderable experience.

Reference Limit Gages. — As mentioned, standard plug or
ring gages made to one size are of little or no practical value in
connection with interchangeable manufacture. Reference gages
should be so made that both the inspection and working gages
can be checked by them from time to time, to prevent the limits

Fig. T. RefercDce Plug Mid Ring Gage

changing due to the wear of the gages. A practical type of
reference plug and snap gage for checking working and inspection
snap and plug gages is shown in Fig. 2. Plug A has nuts on each
end to prevent its use as a working gage. The limits are the
same as on the working and inspection gages. In some plants,
it is the practice to tolerate wider limits on inspection than on
working gages. The reason for doing tbif^ is to reduce the amount
of spoiled work, and also provide for the greater amount of wear
on the working gages. When this system is used, it is necessary
to provide two sets of limits, one for working and the other for
inspection purposes. Reference gages to check the working and
inspection gages should, therefore, be made to take care of this.
The Johansson blocks can be satisfactorily used for this instead
of reference gages.

REFERENCE AND WORKING GAGES

As an illustration, assume that the difference between the
"go" end of the workjng and inspection gages is 0.0005 inch;
that is, the working gage is that amount larger than the inspec-
tion gage. The reference snap gage J5, Fig. 2, can be used to
determine when the working gage has worn down this amount;
as soon as it has, it is turned over to the inspector, and the work-
man is supplied with a new gage. In this way, the workman is
never working to the extreme limits, and the amount of rejected
work is thereby greatly reduced.

Tolerances on Reference Gages. — Gages which are to be
used as standards of reference should be made very accurately.

rOH TtSTINQ
00

IMffr^s-;-

^4H

I 1'

I
I

Machinery

Fig. a. Reference Limit Gages used in testing Limit Working and

Inspection Gages

The permissible tolerances are dependent largely upon the class
of work for which the gages are to be used, as well as the per-
manency of the gages. Some manufacturers make their refer-
ence standards from a good grade of machine or tool steel, and
leave them soft. The reason for this is that soft steel has a lower
coefficient of expansion than hardened steel that is not carefully
seasoned. Soft reference gages are objected to on the ground
that they are subject to wear and are easily dented, and must be
handled with care. The well-known Johansson gages are made

GAGING AND INSPECTION

: nickel steel, and are guaranteed to be within a tolerance
of-o.cx3ooi inch to the inch. This extreme accuracy, however, is
greater than can be ordinarily expected in reguLir reference
gages, and, as a rule, the tolerances vary from 0.00005 ^° 0.0001
for sizes up to i inch, and from 0.0001 to 0.0002 inch for sizes up
to 2 inches. This tolerance on the reference gage is distributed
so as to take care of the wear on the working and inspection
gages which are checked up by the reference gage. For instance,
the "go" ends of a reference plug gage {A, Fig. i) which would
be used for checking the "go" ends of the working and inspection
gages would be made to the required size minus the tolerance.
On the reference snap gage which would be used for testing
working anti inspection plug gages, liie tolerance would be added
to the actual dimension required.

Erroneous Use of Standard Gages. — In some manufacturing
plants, it has been the practice to use standard plug and ring
gages as working gages. In fact, this has been done to such an
extent that a gage on which there is no limit of tolerance is known
as a "fixed" gage and is used in a manner similar to that in which
a caliper is used. There are two reasons why a standard plug or
ring gage should not be used as a working gage. In the first
place, these gages are made very carefully and to extremely
close limits, and if used as a working gage, their accuracy would
soon be impaired. In the second place, as they are not provided
with a working tolerance, a greater amount of tune is consumed
in finishing the work so that the plug will enter or so that the ring
will go over it than would be necessary if a regular limit snap or
plug gage were used. If both the plug and ring gages were used,
they could no longer be considered as standard, as both would
become inaccurate from wear. Furthermore, work which is
finished so thai these gages would fit it would be much more
accurate than would ordinarily be necessary, and the time spent
in bringing it to this degree of accuracy would be wasted. There-
fore, " fixed" gages should not be used for other work than setting
micrometers, calipers, etc.

Limit Working and Inspection Plug and Snap Gages. — The
most common forms of limit working gages are illustrated by the

REFERENCE AND WORKING GAGES

plug and snap gages shown in Fig. 3. The form in which these
gages are made depends to a considerable extent upon the
character of the work. The two types shown at A and B
illustrate common forms of non-adjustable gages. The difference
between the *'not go" and "go" ends on the plug is the maxi-
mimi error tolerated in the hole, and the difference between the
sizes at the two ends of the snap gage, the maximum tolerance
that is permitted on the shaft. The difference between the small
end of the plug and the large or "go" end of the snap gage is the

Yig. 3. Limit Working and Inspection Plug and Snap Gages

minimum allowance between the two parts — shaft and hole —
and the difference between the large end of the plug and the small
end of the snap gage is the maximum allowance between the
two parts, assuming a running fit.

Tolerances on Working and Inspection Gages. — There seems
to be some disagreement between gage manufacturers as regards
the limits on plug and snap gages. Some manufacturers make
all gages within a limit of ±0.0001 inch. This degree of accuracy
is not always necessary, and, where the work can have consider-

GAGING AND INSPECTION

able tolerance, it is desirable not to make the gages to very close
limits; it would be preferable to make the plug gage, for instance.
slightly large, so as to insure long life. The snap gage would be
made correspondingly smaller for the same reason. This practice
is being followed by one prominent concern which has adopted
a unique system of plug and snap gages. The limits on the gages
are governed entirely by the limits on the work. For instance,
where the work must be held to a limit of within ±0,0005 inch,
the limit on the plug or snap gage would be ±0.0001 inch.
Where the limit on the work is ±0.002 inch, the limit on the
gage would be ±0.0005 '"^ch. On extremely accurate work,
where a limit of only ±0.00025 ""ch is allowed, the gage must be

made to a Umit of ±0.00005 inch. This means that the life of
the gage is considerably shortened.

Setting Tolerances on Working and Inspection Gages. — As
an illustration of the point mentioned. Fig. 4 shows a plug and
snap gage used in producing a shaft and hole that were required
to have a good running fit. In this case, the maximum allowance
between the largest shaft and the smallest hole is 0.003 inch, and
the minimum allowance is 0.001 inch. The maximum tolerance
on the shaft b o.ooi inch and the same tolerance is allowed in
the hole. The difference, therefore, between the "go" and
" not go " sizes on the snap gage is 0.001 inch. In manufacturing
the snap gage, the "go" portion is made to a limit of 0.99&5

! , ' ^ i . This provides o.oooi inch for wear before the
j + 0.0000 S

gage would be worn down to the size indicated. On the "not
go" end, it is not so important whether the limit is set plus or
minus, although it is preferable to have it minus, which would
prevent work ahnost up to the "not go" size from going in. On
the plug, the "go" end is made o.oooi inch large to pro\ide for
wear, and the "not go" end is made this amount small. In this
way, the manufacturing limits are set so that the life of the gage
will be increased without affecting the interchangeability of the
work.

Advantages of Tool-setting Gages. — In working to limit
gages, the tendency is for the operator to work as close as possible
to the "go" end of the gage for fear of spoiling the work. This
results in the parts going together with the minimum of freedom.
The object, however, is to make the parts to the mean dimen-
sions. Tool-setting gages which generally consist of hardened,
ground and lapped blocks are used to set the cutting tools, and
are made to the "mean dimension." These are used in connec-
tion with a hardened and ground locating block on the jig or
fixture, and are employed principally on pro&ling and milling
fixtures.

Life of Plug, Ring, and Soap Gages. — The life of a gage is
governed by many conditions, among which might be mentioned:
Tolerance allowed for wear; condition under which gage is used,
whether for manufacturing or inspection purposes; character of
material on which gage is used, whether brass, jast iron, steel,
etc.; condition of work on which gage is used, that is, whether
rough-turned, finish-ground, lapped, etc.; material from which
gage is made, whether cast iron, carburized machine steel, tool
steel, malleable iron, etc.; condition of measuring surface on
gage, whether ground or highly finished and lapped; care used
in applying gage.

Tolerance for Wear. — As mentioned, limit gages are usually
made with Umits that increase the life of the gage. In other
words, on a plug gage, the "go" end is made with a limit larger
than the size specified on the gage. The amount of this limit, in
a general way, determines the life of the gage. As a case in
point, on one extremely accurate piece of work, a limit of 0.00025

fllB

' 54

GAGING AND INSPECTION

inch was the greatest tolerance. The plug gage was, therefore,
made with a plus wear limit of D.00005 inch, and as this gage was
used in testing a hole finished by grinding, where considerable
grit and dirt accumulated, its life was only one day of ten hours.
In other words, a new gage had to be furnished every day. This,
however, is an exceptional case, but it serves to illustrate the
necessity of setting limits on the gage to provide for wear. TTie
greater the limits on the work, the larger can be the tolerance for
wear on the gage, so as to increase its life as much as possible.
Furthermore, when the "go" end of a plug gage, for instance,
is made larger than the lowest limit of tolerance, the machine
operator is working closer to the mean or nominal dimension.
In purchasing gages, most manufacturers do not give the subject
of wear the attention it deserves, and generally demand of the
gage-maker the exact sizes given, which do not provide for wear.
This results in greatly increasing the gaging and inspection
expense.

Conditions under which Gages are used. — The conditions
under which a gage is used, that is, whether it is used for manu-
facturing or inspection purposes, governs, to a large extent, the
number of pieces that can be gaged. It is, therefore, the practice
of some firms to permit a larger limit on the working than on the
inspection gages, and then interchange these gages as they begin
to wear. For example, in one plant the machine operator is given
the newest gage when it is of the plug variety, and the oldest
when of the snap variety (solid type), and to keep close watch
on the condition of the gages, this firm employs several men,
known as "field" inspectors. The duties of these men are to
cover the entire plant, inspecting the gages and replacing those
that are worn out by new gages adapted lo the work. When a
job is turned in and the gages and tools sent with it, these gages
are not allowed to be put in the tool storage or supply room, but
are handed over to the field inspectors, who carefully go over the
gages before they are stored. These field inspectors also see
that the production and inspection departments are supplied
with the proper gages. In this way, the machine operator is
always provided with a gage with the closest limits, and, con-

sequently, the greatest amount of wear is obtained from the
gages. Gages wear much more rapidly when used for manu-
facturing than when used for inspection purposes, so that the
interchange of gages greatly reduces the amount of rejected work.

InSuence of Material being Gaged on Life of Gages. — The
kind of material being gaged also has considerable bearing on the
number of pieces that tan be gaged before the gage is worn be-
yond the required limits. Some materials, such as cast iron and
aluminum, have a lapping effect, and wear the gage much more
rapidly than either brass or steel. In one plant where a large
number of aluminum fuse parts are manufactured, a careful
inspection of the gages proved that in gaging 10,000 aluminum
parts the wear on the gage was 0.0005 inch. It was also found
that five times as many brass parts could be gaged with the same
amount of gage wear; in other words, the same gage used on
brass would inspect 50,000 parts before it was worn 0.0005 inch.
Cast iron has a lapping effect somewhat similar to that of alu-
minum, but not so pronounced. In gaging cast iron, about
20,000 parts can be gaged with a wear of 0.0005 inch on the gage.
The wear depends to a considerable extent upon the diameter of
the work and its condition when gaged.

Influence of Condition of Work on Wear of Gsges. — The
condition of the work — whether rough or smmth — also has
a governing effect on the life of the gage. Rough-turned work
will wear a gage more rapidly than a ground surface, free from
grit. As an indication of the Ufe of an ordinary snap gage on
work that is ground fairly smooth, it was found in one plant,
where a careful record was kept, that 35,000 Russian shrapnel
shells having a ground surface could be inspected with one gage
before it was worn beyond the required limit. In this particular
gage, 0.002 inch was allowed, for wear, so that the gaging of
35,000 shells removed this amount of material from the surface
of the measuring point on the gage. In tliis plant it was also
found that solid snap gages did not give nearly as satisfactory
service as those that were made with adjustable points. The
latter could be readjusted every day to a standard plug, and the
life could thereby be greatly increased. In another plant where

GAGING AND INSPECTION

a similar limit was allowed on the gage and where the work was
turned instead of ground, the number of parts inspected varied
between 8000 and 10,000 before the 0.002-inch limit was re-
moved from the surface of the gage. This shows that ground
work has not nearly as abrasive an effect on the gage surface as
rough-turned work; speaking in approximate terms, a gage can
be used for on!y about one-third as many rough-turned pieces as
it can for ground pieces.

Material used for Gages. — Gage-makers differ to a consider-
able e-xtent in regard to the material from which gages should be
made and its bearing upon the life of the gage. There are so
many points to take into consideration in this connection that
it is difficult to reach any definite conclusion. For instance, one
point that must be considered is the total number of parts to be
gaged; another, conditions which would make it unnecessary to
inspect every part; still another, whether the gage is to be used
for reference, working, or inspection purposes. It is generally
conceded, however, that for plug gages used for manufacturmg
purposes, it is preferable either to make the gage from a good
grade of machine steel and -carburize it, or to make it from tool
steel, hardened, seasoned, ground and lapped. Gages are seldom
left soft unless they are used for reference purposes, or unless only
a few parts are to be inspected. It is also the practice to leave
thread gages soft.

The type of gage also has an important influence on the
selection of material from which it should be made. For in-
stance, a solid snap gage is seldom made from cast iron, either
a malleable casting or a steel forging being used. Most manu-
facturers of solid snap gages make them from drop-forgings,
when they are used for measuring up to 3 inches in diameter.
Above this size, the gages are made from steel castings which
are heat-treated, seasoned, ground and lapped to siie. When
snap gages are provide<l with adjustable points, it is the gen-
eral practice to make the frame either from malleable cast-
ings or from cast iron. One prominent manufacturer of snap
gages follows the practice of making the frame from cast iron
of frail dimensions. This is done so that, in case the gage is

^^^K^

REFERENCE AND WORKING GAGES

dropped on the floor, the frame will break rather than distort.
In this way, any chance of the operator distorting his gage
without knowing it is eliminated. The frame is also made of
such a shape that it is impossible for the operator to "peen"
the gage to fit the work. The difference between the lives
of a solid snap gage made from iine-graincd cast iron and one
made from Iiardened steel is considered by many gage-makers
to be e.\tremely slight.

Condition of Measuring Surface and Life of Gages. — The
condition of the measuring surface on the gage is not always
considered a vital factor affecting the life of the gage. When
it is understood, however, that it is practically impossible to
secure a perfectly plane surface, the question of securing a
smooth surface on the gage appears to be of greater impor-
tance. Some gages, especially the Johansson gages, have the
property of adhering when wrung together with a force con-
siderably greater than that due to atmospheric pressure on the
areas in contact. This phenomenon has been attributed to
molecular attraction, but investigation has shown that the
adhesion is due to the presence of a very thin liquid film.
Blocks made from hardened steel were prepared, each weighing
an ounce and a half and having surfaces 0.7 square inch, polished
flat to within ^^„|„^,f, inch of being a true plane. These blocks
were then used to test the adhesive properties of different
liquids. The contact faces were carefuUy freed from moisture
and cleaned witii alcohol. When the blocks were wrung to-
gether, they fell apart under their own weight, but as soon
as a film of oil or other liquid was put between them, a force
of 17 pounds for Rangoon oil, 20 pounds for lubricating oil.
29 for turpentine, and 35 for condensed water vapor was re-
quired to separate the blocks. From this test it was proved
that it is impossible to obtain perfect union between two parts,
and tile only reason that they held together was because of
the adhesive qualities of the lubricant or other hquid. Any
machined surface, no matter how smooth, consists of humps
and hollows, so that a surface which is brought down to the
closest approximation of a true plane is one in which there

GAGING AND INSPECTION

would be the greatest number of points in a common plane.
It is, therefore, reasonable to assume that a gage made with

Table L Estimated Life of Gages Used for 4.7-inch High-explosive

SheUs

operation

Type of Gage

Estimated Life —
Pieces Gaged

Rough Blank

Length of billet

Crescent

100,000

Diameter of billet

Crescent

100,000

Forged Blank

Diameter and length

Templet, snap

10,000

Cavity

Plug, flat

10,000

Diameter

Crescent

100,000

Wall thickness

Caliper

50,000

Length, total

Flat hook

100,000

Shell Body

Trim base

Plunger, depth

30,000

Trim length

Fixture

30,000

Form nose

Flat, profile

11,000

Nose diameter

Crescent

100,000

Nose diameter

Ring

25,000

Body diameter

Crescent

100,000

Base diameter

Crescent

100,000

Band groove

Crescent

100,000

Base groove

Crescent, special point

100,000

Base groove

Flat, snap

5.000

Base groove

Flat, profile

11,000

Crimping groove

Flat, profile

11,000

Band groove

Flat, profile

11,000

Width band groove

Flat, limit

25,000

Base to bourrelet

Flat, profile

100,000

Bore for thread

Limit, plug

25,000

Thread recess

Flat, location

11,000

Thread plug
Counterbore

Limit

4,000

Limit, plug

25,000

Wall thickness

Concentric special

50,000

Band profile

Flat, limit

11,000

Base diameter

Ring gage

25,000

Diameter over band

Ring gage

25,000

a smooth measuring surface will wear much longer than one
made with a rough surface.

Ill

RKFERENCE AND WORKING GAGES jg

Care used in Applying Gages. — II has been previously
stated that gages used for inspection purposes wear much longer
than those used as working gages. One reason for this is that
the inspectors handle the gages much more carefully than do
the workmen. In the first place, an inspector is seldom put
on a piece-work basis, whereas a machine operator usually is.
The chief point with the workman is to turn out as many parts
as he can in the shortest possible time.. To show that this is
the case, a prominent concern made a careful test of the gages
used by an experienced inspector and found that in inspecting
130,000 pieces the different gages were worn from 0.0015 to
0.003 inch. Similar gages used for manufacturing purposes
were found to last only one-half as long as those used in the
inspection department.

Life of Gages used on Ammunition Work. — The production
of munitions in the United States has caused considerable
attention to be paid to interchangeable manufacture and the
use of limit gages. Parts for shells, fuses, etc., have been made
by several different firms and then assembled in a separate
plant, so that each part had to be made a duplicate of the other
in order to enable assembling without tilting. Hence, each plant
had to be equipped with a complete set of limit working and
inspection gages. Several interesting points have come up in
connection with the design and use of gages, one of which is
the length of time that a gage can be used before it is worn
beyond the set limits of tolerance. Some manufacturers did
not equip their plants with the necessary number of reserve
gages, with the result that they had to wait for a considerable
length of time for deliveries from gage manufacturers. On
account of this trouble, a close record was kept of the life of
various gages, so that considerable data were soon available.
Wells Bros. Co., of Greenfield, Mass., collected a large amount
of information on this subject, some of which is presented in
Tables I and 11. The number of pieces tested by the various
gages is based on data obtained from various munition manu-
facturers and represents a safe estimate of the approximate
life. It should be noted in this connection that in very few

GAGING AND INSPECTION

Table II. Estimated Life of Gages Used for 4.7-inch Hic^-explosive

Shells

operation

Type of Gage

Estimated Life —
Pieces Gaged

Band

•

Cut length
Wall thickness

Fork, limit

100,000

Fork, limit

100,000

Chamfer

Flat, profile

11,000

Hole

Plug, limit

25,000

Base Plug

Large diameter

Crescent

100,000

Thread diameter

Crescent

100,000

Concentricity diameter

Thread ring

20,000

Thread and groove

Crescent

100,000

Length thread and head

Flat, profile

11,000

Counterbore

Limit, cylinder plug

25,000

Thread bore

Limit, cylinder plug

25,000

Thread

Limit, thread plug

4,000

Thread and groove

Flat, location

11,000

Depth and width, slot

Special plug

25,000

Outer thread diameter

Crescent, thread

100,000

Iron

or Dronzc Fuse Hole Plug

Head diameter

Fork, limit

100,000

Flat for wrench

New Corey, limit

100,000

Thread and groove

Fork, special point

100,000

Thread outside diameter

Fork, limit

100,000

Concentricity

Ring, thread templet

' 20,000

Length and shoulder

Flat, limit

11,000

Internal thread groove

Flat, limit

11,000

Thread size

Fork, thread

100,000

(Alternative) Die-cast Fuse. Hole Plug

Head diameter

Fork, limit

100,000

Socket

Plug, limit

25,000

Thread diameter

Fork, limit

100,000

Concentricity

Ring, thread templet

20,000

Thread in groove

Fork, special point

100,000

Length and shoulder

Flat, limit

11,000

Thread size

Fork, thread

100,000

REFERENCE AND WORKING GAGES Si

cases were the gages provided with any tolerance for wear,
so that their life was considerably shorter than would have been
the case if a percentage of the tolerance on the work had been
placed on the gage.

T]rpes of Plug Gages. — Plug gages are made in a variety
of forms and sizes, depending largely upon the shape and size
of the work to be measured. For gaging small holes, they
are generally made from a solid piece of steel, whereas for
gaging larger holes, they are built up and so constructed as to
make them easy to handle. A reference standard plug gage
of the type shown at A in Fig. 5 is used chiefly for sizes up to
I inch in diameter. For larger sizes, the gage generally has
the form shown at B, and is made of a flat section from either
a drop-forging or a steel casting, ground and lapped on the
circular contour. The gages shown at .-1 and B should not be
used for working or inspection gages, but merely for reference
purposes.

At C is shown a simple form of limit plug gage for compara-
tively small work, This consists of a hexagon handle provided
with tapered holes in each end, into which hardened, ground
and lapped plugs are fitted. The "go" plug is made consid-
erably longer than the "not go" plug, tu distinguish between
them. Another type of plug gage shown at D is used for work
of larger diameter, generally up to about i inch. This gage
also has one end longer than the other, the longer being the
"go" end of the gage. When a gage of this type is used on a
grinding machine, the operator does not know how much ma-
terial is to be removed until the "go" end enters the work. For
this reason, it is the practice in some plants to taper the "go"
end of the gage as indicated by the dotted lines a, making the
end from 0.005 t" o.oio inch smaller than the regular "go"
size or straight portion. This enables the operator to enter
the gage into the work after he has taken his first roughing
cut, and he can thus work much more rapidly; the chances
of grinding the hole too large are also reduced, and at the same
time the gage does not have to be used so frequently. When
a plug gage of this kind is used, it is advisable to have the limit

GAGING AfTD INSPECTION

on the "go" end as close as possible to the mean dimension
and have the greater amount of tolerance on the "not go"
end. The reason for this is that it is easier for the operator
to work to the "go" end with this type of gage, and as it is
the mean dimension that is always desired, it is advisable to

Fig. 5. Types of Plug Gages

have the limit here as close as practicable. Say, for instance,
that the total tolerance between the "go" and "not go" ends
is 0.002 inch; then the limit on the "go" end should be 0.0(3035
inch below the mean dimension and the remainder of the tol-
erance should be on the "not go" end.

REFERENCE AND WORKING GAGES 63

It is the practice of some manufacturers to make a gage
of this sort single-ended and use the taper as a limit, This
practice is not recommended for the reason that, if the cylin-
drical part of the gage enters the hole, it would be too large.
Consequently, it is necessary to have the plug enter to about
one-half the way up the taper. This does not give the operator
a chance to tell whether he has a bell-mouthed hole or not.
Neither does it give him a chance to determine if the hole is
truly cylindrical or tapered unless he removes it from the chuck
and tests both ends.

When the work has a hole passing through it, the plug gage
is sometimes made of the type shown at E. This gage has an
advantage over that shown at D in that the "go" and "not
go" sizes are on the same end of the gage, so that the operator
is not likely to use one for the other. In order to facilitate
grinding a hole to the correct size, the end of this plug gage can
be tapered similarly to that shown by the dotted lines a, at D.
An improvement over the gage shown at E is shown at F\
this gage can only be used where the hole passes completely
through the work. Here the gage is provided with three di-
mensions; first, the "go," second, the "mean" or exact di-
mension desired, and third, the "not go." In all manufac-
turing, especially on close work, the mean dimension is the one
desired, and having a gage made with the three sizes, low,
mean and high on one end, it is easy for the operator to work
to extremely close limits with comparatively little trouble.

As a matter of fact, however, the plug gage is not a true
detector of all the errors in the hole; for instance, a plug gage
will not indicate whether or not the hole is truly cylindrical.
It merely tests whether the hole is of the required size at a
certain point, and for the majority of work this is sufficient.
With a plug gage made as shown at G, it is possible to tell
whether the hole is round or not within the required limit.
The "mean" and "not go" shoulders are ground flat as shown, so
that only two points of the circumference are to the required size.
By turning the gage around, it is possible to determine the
truth of the hole. This gage has been found satisfactory where

64 GAGING AND INSPECTION

an extra degree of refinement is necessary and where the hole
is not "three-cornered." This condition is only found when
grinding work that is not properly balanced.

The gages shown from C to C are for inspecting small-sized
holes up tu I inch in diameter. When the holes are greater in
diameter, a built-up gage is preferable in order to economize
stock. One type of built-up gage is shown at /. This gage
consists of "go" and "not go" cylindrical plugs fitted onto
a soft steel shank by simply having the turned-down end of
the shank slightly tapered and driving on the rings. This is
a comparatively cheap gage to manufacture, and is satisfac-
tory for the majority of work. Another type of built-up plug
gage for large work is shown at /. In this case, the handle
is made an easy fit in the holes of the "go" and "not go" plugs;
the latter are fastened to the handle by means of screws, as
shown, and are prevented from turning by pins which fit in a
slot in the hole in the gage plugs. This type of gage is more
expensive to manufacture than the type shown at /, but there
is no danger of the plugs turning around or coming off while
in the work. At A' is shown a type of plug gage for gaging
very large holes. The "go" and "not go" plugs are lightened
by drilling six holes around the plugs midway between the
outer circumference and the hole, A gage of this type must
be carefully hardened to prevent cracking, and also seasoned to
eliminate any internal strains that might develop after the gage
had been in use.

An unsuccessful attempt to lighten a plug gage is shown at L.
This type of gage has many disadvantages, one of which is the
difficulty of hardening without springing it out of shape. Also,
owing to the unequal strains set up in hardening, which are
only partially removed by seasoning, it will not retain its shape
when in use, and soon becomes out-of-round and inaccurate,
rt is also more affected by temperature changes than solid gages.
A plug gage of this shape wiiich is held in the hand for a few
minutes will be found to be out of round about 0.0005 '"ch,
simply because of the strains set up and the lack of sufficient
support at the outer end. This gage is much lighter than a

REFERENCE AND WORKING GAGES 65

solid gage, but the objections are so great that it is not recom-
mended, although it has been used to some extent.

A gage which is made in a somewhat similar manner, but
is so constructed that the strains are equaUy divided, is shown
at M. Here the "go" and "not go" plugs are counterbored,
and the mass of material is in the center. In hardening, the
strains are more equally distributed throughout the mass, and,
by careful tempering and seasoning, can be practically elimi-
nated. The gage is also lightened by making the handle hollow,
as shown. This type of construction is used by C. E. Johansson,
maker of the well-known Johansson gage blocks. The hollow
handles allow the air to pass through the gage when gaging
blind holes, and the plugs are reversible, insuring long life.
The measuring plugs are made of high-carbon Swedish crucible
steel, hardened clear through and tempered and seasoned. The
operations on these plugs consist in hand-forging, roughing to
shape, hardening, tempering, rough-grinding, seasoning for a
long period, and finally grmding and lapping. It is also claimed
by this concern that making gages from low-carbon steel, case-
hardened, is unsatisfactory, due to two causes. One is the
rapid method of seasoning which is generally employed, and
the other, the constant pulling of the hard case on the soft
core. Gages that are hardened all through and carefully
seasoned are not so likely to change as those that are c
hardened and improperly seasoned.

Very large plug gages are made of a type somewhat similar
to that shown at B, except that they are provided with two
diameters giving the plus and minus limits; or they are made
of the bushing type shown at N, having an aluminum core
and handle. A gage made of this type must be carefully
hardened, and seasoned for a considerable period. It is also
inadvisable to drive the sleeve onto the aluminum core. A
better method is to hold the sleeve on the aluminum core by
means of screws, as shown. This prevents distortion of the
ring. The ring should be finish-ground and lapped while it
is attached to the aluminum core, so as to prevent any liability
of distorting it by assembhng after lapping.

REFERENCE AND WORKING GAGES 67

Another plug gage which is comparatively cheap to manu-
facture, and also very accurate, is shown at H. This consists
of two balls which are electrically welded to a handle. (One
end of the gage only is shown ii\ the illustration.) This gage
has one serious disadvantage, in that its Hfe is comparatively
short, owing to the line contact which it presents to the work.
There are many other types of plug gages used in various plants,
but those shown in the foregoing illustrate the general prin-
ciples of construction.

Types of Snap Gages. — Snap gages used in general manu-
facturing are made in three typ&; namely, solid, adjustable,
and built-up gages. The adjustable type consists of a frame
having adjustable anvils, and the built-up type is made from
separate blocks. One type of snap gage, which is shown at
A in Fig. 6, is known as a standard or reference gage. This
gage is not provided with any working limit and is made to
standard size, being used for reference purposes only. It is
usually made from a high-carbon steel forging, carefully hard-
ened, seasoned, ground on the measuring faces, and lapped.
The use of this gage for other than reference purposes should
be discouraged.

A type of gage which is a combination of snap and plug
gages is shown at B. This is made and used in the same way
as gage A. At C is shown a common t>-pe of limit snap gage
which is made from sheet steel, varying in thickness from \ to
\ inch, depending upon the diameter and character of the work
being gaged. Snap gages of this type should have as wide a
bearing surface as possible, as this greatly increases their life.

Another type of limit snap gage which is usually made from
a forging, although sometimes from a malleable casting. Is
shown at D. This gage is made in two principal forms, one
being shown by the fuU outline and the other by the dotted
outline a. The dotted outline type of gage is used when the
diameter to be measured is greater than i inch. Making a
gage to this shape lightens it considerably. A single -ended
type of limit gage is illustrated at E. This is provided with
one flat jaw and one having the permissible tolerance on it.

Gages of this kind are usually made from drop-forgings and
hardened. At F is shown a limit snap gage in which the body
is made from cast iron with solid measuring points inserted.
This gage is not provided with any adjustment, and it is
necessary to renew the points when they become worn. This
type is used only on very large work.

Another type of limit gage having only one Jaw, but being
provided with adjustable points, is shown at G. The adjust-
able points are prevented from turning in the holder by means
of screws, as shown, the points having a flat side against which
the heads of the screws restT The anvils are adjusted in and
out by means of the headless screws and are clamped by the
screws passing through at right angles to the axis of the anvils.
The forward faces of these anvils are beveled to prevent mar-
ring the work. Usually, on an adjustable snap gage of this
kind, the points are not made absolutely flat, but are slightly
convex. This insures that the measurement is always taken
directly on the axis of the adjustable plug.

Still another type of adjustable point measuring gage, in
which all four measuring points are adjustable, is shown at H.
This type of gage is the Johansson patented limit adjustable
snap gage. The measuring plugs are not threaded and do
not turn in the body, having an end movement only, which
prevents any possibility of their becoming cocked, as is the
case with threaded plugs. They consist of plain cylinders of
hardened steel, with flats on one side, and are lapped a snug,
sliding fit in the lapped holes in the body. The ends which
come in contact with the work and the faces of the adjusting
screws are lapped square with the axis. The flat surface on
the plugs and clamping screws prevent the plugs from turn-
ing in the body when adjustments are made. The rear end of
each adjusting screw is provided with a screw driver slot, and
the forward ends which come in contact with the plugs are
lapped square with the axis. These screws should be sealed
by the inspector after the gage has been set, to prevent the
workmen tampering with it. The clamping screws are so
arranged that they not only clamp the plugs, but also tend

REFERENCE AND WORKING GAGES

to force them to a seat on the adjusting screws. The body
of the gage is made from an iron casting of comparatively
frail dimensions, so that, if it should be dropped, it is more
likely to break than to be distorted. The frame is provided
with an insulated rubber grip to prevent the heat of the hand
from affecting the accuracy of the gage. By holding the gage
with two fingers on the insulated grip, a sensitive touch can
be attained, and at the same time the gage will not be distorted
by the heat from the hand.

In using double-ended lunit gages of the type shown at D,
where the "go" end passes over the work, the gage will soon
become inaccurate unless handled carefully, owing to the ham-
mer effect on the throat of the gage when it hits the work.
This causes a peening action which gradually o\Kns the jaws.
Different devices have been used for overcoming this. One,
which is sliown at I, consists in using a rubber pad fastened
to the throat of the gage, as indicated. This takes the shock
of impact of the gage on the work and prevents the peening
action. Another method is shown at J, which consists of in-
serting a spring plunger in the throat of the "go" end of the
gage. The "not go" end need not be made in this manner,
as it is not supposed to pass over the work.

Rapid Inspection Limit Snap Gage. — A type of limit snap
gage provided with an extension jaw, and which can be used
either as a working or inspection gage, is shown in Fig. 7. This
gage, which is patented by Wells Bros. Co., Greenfield, Mass.,
consists of a frame carrying a hardened, ground and lapped
anvil plate and two adjustable measuring points. For snap
gages having a capacity up to ij inch, the frame is made from
a drop-forging, while, for larger sizes, malleable castings are
used. In the rear end of the frame is a hole which is elongated
on the larger sizes to faciUtate holding; there is also an exten-
sion base A, which can be used for holding the gage in a
stand when it is desired to use it for inspection purposes. The
lower jaw carries a hardened, ground and lapped anvil B, which
is held in place by two screws as shown. This anvil greatly
facilitates the location of the gage on the work, and makes

rapid inspection possible. The measuring points C and D for
the "go" and "not go" sizes, respectively, are hardened,
ground and lapped on the circumference and ends. The plugs
are adjusted by screws E and F, and are clamped by a bar
G and screw H.

Built-up Limit Snap Gages. — In many plants, and espe-
cially in those industries where a limit gage system is used
extensively, considerable use is made of the built-up type of
snap gage, one form of which is shown at K in Fig. 6. This

Tig. 7- Wen* Btoc.

Rapid iDSpectioo Limit Snap Gage

gage consists of three members — one center spacing block
and two measuring blocks. The form in which these meas-
uring blocks are made differs in various plants. In some cases,
one of the measuring blocks is split in half and the limit pro-
vided by grinding down half the center block the required
amount for the "not go" end. The other system, which is
shown at K, consists in having the limits on one of the
measuring blocks. This type of gage is comparatively cheap
to manufacture, as it can be finished complete on the surface
grinder and is easily built up and taken apart for different i
^zes; it is only necessary to change the center block and the 1

REFERENCE AND WORKING GAGES

tolerance on one of the side blocks to adapt it for different
sizes. A brass plate b is fastened under the head of the screws
to carry the job number and any other necessary data. It
is the practice in some plants to put the "go" and "not go"
dimensions on this piece, so that the operator knows what
dimensions he is working to. Usually, however, this piece
simply carries the job number, and is substituted by another
when the gage is built up for a different size.

Table m

Proportion, for Buil

-up Umit Soap GtgBE

l^^^pLlU 1

1^ "■'

.f^P 1

^^. BRASS PLATE

"»

■ r. 1L1.^U4

^- ^v^v-feri-

' ll<u*ln,n,

— 1

•

■>

H
H
)*
1^1

H
it

1^1

Proportions for BuUt-up Limit Snap Gages. — Tabic III
pves proportions for standard parts of buDt-up snap gages
of the type shown at A' in Fig. 6. This gage, as the table
shows, is made in five sizes. The spacing blocks are made
from machine steel and vary in thickness by j'j inch; that is,
the space between the maximum and minimum sizes B and C
for each number of gage is divided into thirty-seconds of an
inch. Hence, eight spacing blocks would be needed for gage
No. 2. These spacing blocks are casehardened and ground
and have the size stamped in the clearance cut. The top

GAGING AND INSPECTION

block, a is ground parallel, while the bottom block b is made to
provide for the tolerance on the work and is stamped accord-
ingly. Both these blocks are made from tool steel and hard-
ened. When a snap gage of a certain size is desired, two blocks
a and b and a spacer of the required thickness are obtained
from the store-room and fastened together by screws which
are standardized. A brass nameplate carrying the piece and
operation numbers is put on, thus obviating the stamping of
the gage proper; when worn, the gage can be taken apart,
ground, lapped and put together again, and used indefinitely.
The advantages of this type of snap gage for interchangeable
manufacturing are obvious.

Taper Plug and Ring Gages. — The measuring of taper holes
is practically always a fitting proposition. In fitting taper
parts, the points that receive attention are the taper per foot
or inch and the relative longitudinal positions of the two parts
which fit together. In making a taper fit, the largest diameter
of the hole and the largest diameter of the shaft must corre-
spond within certain limits, these limits being measured length-
wise along the taper. The limits of tolerance allowed on a
taper fit are dependent upon the taper, the methods used in
holding the tapered parts, and their relative positions. The
limits for a taper fit are seldom less than o.oto inch, longitu-
dinal dimension, and may be as much as J inch on slight
tapers.

Reference Taper Plug and Ring Gages. — The gages used
for inspecting taper shafts or holes are usually of a simple type,
the test being made largely by applying Prussian blue to either
the plug or the ring; especially is this necessary when testing
the degree of taper. Fig. 8 shows standard or reference taper
plug and ring gages. The standard plug, as a rule, is provided
with two or more shallow grooves to catch dust and dirt. The
ring is abo made with grooves, in some cases. When a taper
plug is to be made for a standard taper, such as the Brown &
Sharpe, Morse, Jarno, etc., the plug is made to the exact length
specified, and the largest and smallest diameters on the plug
are checked within limits very close to those given for the

different numbers of tapers. The same, of course, applies to
the ring. When a plug is to be made for other than what is
known as "standard" tapers, the size of the large end and the
amount of taper are the only two governing points.

Setting Limits on Taper Gages. — As mentioned, the two
chief points to consider in securing a taper fit between two
parts is the fit of the taper and the relative longitudinal posi-
tions of the parts In most cases, the largest diameter is taken
as the standard size but there are exceptions to this rule. As
it IS seldom necessarj to have a taper end exactly at a shoulder
on average mactune work, the tolerance is, as a rule, not held
to very close limi ts There are cases, however, when the longi-
tudmal position of one part on another must be held to close
limits and when this is the case, great care should be taken

Reference Taper Plug ■nd Ring Gage

in setting the limits of tolerance. Knowing that it is possible
to work to limits of ±o.ooi inch on cylindrical work, this is
also possible on taper work. Knowing also the tolerance on
the longitudinal distance, the distance which governs the posi-
tions of the "go" and "not go" points for the various tapers
per foot may be obtained from Table IV. This table forms
a basis for the location of the limit points. For example,
assume that the taper on a shaft and hole which must go to-
gether is f inch to the foot, and that these two parts must be
made on a strictly interchangeable basis in large quantities.
Assume also that the relative longitudinal po.sition of the two
parts is not highly important. The question to be settled is
the distance between the "go" and "not go" points on the
male and female gages, respectively.

In order to provide as wide a limit as practicable, assume
that the maximum tolerance for the hole and shaft, respec-

GAGING AND INSPECTION

tively, is o.ooi inch. In other words, assuming that the nomi-
nal size is 1.500, the largest hole would be 1.501 inch, and the
largest diameter on the smallest shaft, 1.499 inch. This gives
an allowance between the diameters of the largest hole and
smallest shaft of 0.002 inch. Hence it is necessary to know
what longitudinal tolerance this represents in order to fix the
limits on the male and female gages. Referring to Table IV,

] Differeace of

T
i

... "°'""'"

MaMHtn

T.„„,W

Inchei

TapB-perPrnt

Inches

0.062s (locomotive work)

0.1150 (shell reamer arbors)

0.1875

. 3500 (standard taper pins)

0.3750

°S^ (Brown &Sharpes'f(i)

o-5«o

5910 (American s'l'd)

0.5910

0,6000 (Morse & Jarno s't'd)

0640
04»o

03 JQ

0340

02J3
OlOi

0.60J0 (Morse a'fJ)
0.6210 (American s't'd)

6300
0,7500

1.13SO

i,tS'»

i.sooo (S. A. E. sVd)

3,0199
J.019J
j,oi9i
1,0191
>,oi9i

.0106
.0096
.0080

it will be noted that, for a difference of o.ooi inch in diameter,
the length of the taper is 0.016 inch; hence, for a difference of
0.002 inch in diameter, the length of the taper is 0.032 inch.
This amount is, therefore, the distance between the limit points
on the male and female gages. When the taper is slight, say
0.350 inch to the foot, the length of the taper for a difference

REFERENCE AND WORKING GAGES

of o.ooi inch in diameter holds good only when the parts are
put together without pressure.

Reference to Fig. 9, which shows various types of limit taper
plug and ring gages, will show how the limit for longitudinal
position is set. In the case shown at B the plug has two lines
on it, the lower one of which is the "go" and the other the
"not go" position. The ring is cut away, as illustrated, and
also has two lines on it, the lower one being the "not go" and

Different Trpei of Taper Plug 4nd King Giges

the other the "go" position. In setting the limits on the plug
and ring gages, respectively, the "go" position on the plug
should correspond exactly with the "not go" position on the
ring. In other words, when the ring is placed over the taper
plug, the "not go" line on the ring should coincide with the
"go" line on the plug.

The kind of iit is governed by the amount of taper given
to the part. For instance, on taper pins which will not work

76 GAGING AND INSPECTION

loose, the amount of taper varies froifl -^g to \ inch to the foot.
For sockets which are required to drive cutting tools, the tapers
vary from 0,500 to 0.63a inch to the foot. For locomotive
frame bolts, the taper is generally -^ inch to the foot. For
arbors which carry shell reamers, etc, the taper is 5 inch to
the foot. For general automobile work, the accepted taper is
i§ inch to the foot. When the longitudinal movement of
two parts that go together is not to be greater than 0.010 inch,
a taper not less than 1 1 inch to the foot is necessary, whereas,
if a longitudinal distance has a tolerance of ^5 inch, a taper
as small as ^ inch to the foot would be satisfactory, when the
longitudinal position Is the only factor that need be considered.

Types of Taper Plug and Ring Gages. — The taper plug
and ring gage shown at A in Fig. g is used only for reference
purposes; B shows a type of taper plug and ring gage in which
the limit is indicated by two lines. Another type of taper
plug and ring gage is shown at C. Here, instead of having the
limit lines on the plug and ring, the two members are milled
down as shown, the distance between the two milled cuts being
the amount of tolerance on the work. Another type of limit
plug and ring gage is shown at D. In this case, the plug
consists of a handle to which two bushings are attached, which
are ground to the correct taper. With this type of plug, it is
a comparatively simple matter to obtain a correctly machined
taper hole without the use of Prussian blue or other fitting
pastes. The taper in the hole can be easily tested by the
wabble of the plug, as it rests in the hole at two points only,
instead of its entire length. A similar idea is carried out on
the ring, which is cut away and relieved in the center as
iliustrated.

In using plug gages of the type illustrated at B and C, diffi-
culty is sometimes experienced, especially when the taper is
slight, due to the plug "sticking" in the hole. One way of
eliminating tJiis is to make the plug as shown at D, but prob-
ably a more satisfactory way is to make it as shown at E,
Here the plug is slabbed down on both sides, which allows free
passage of the air; this will be found especially advantageous

REFERENCE AND WORKING GAGES

in gaging blind holes. The only <iisadvantage of this plug is the
difficulty of lapping it accurately. At the right-hand side of
the illustration at E is shown a method of using two straight-
edges for testing a taper. This type of gage is generally used
on the bench, being mounted on a stand, and is especially
useful for originating tapers. In connection with two hard-
ened and ground disks, as shown by the dotted lines, these
tapered straightedges can be set very accurately to any degree
of taper desired and used as a standard, if a standard plug gage
does not happen to be available. When great accuracy is
required in the measurement of tapers, this type of gage may
be employed. It will be seen that if two disks of unequal
diameters are held in contact or a certain distance apart, lines
drawn tangent to their peripheries will represent an angle or
taper, the degree of which depends upon the relative diameters
of the disks and the distance they are placed apart. Referring
to £ in Fig. g, assume that it is required to set the gage to a
taper of | inch to the foot, and that the disk a is 1.5 inch and
b, 1.2$ inch. It is desired to find the distance c, or the center
distance between the two disks.

Rule: — Divide the taper [>er foot by 24 and find the angle
corresponding to the quotient in a table of tangents; then
find the sine corresponding to this angle, and divide the dif-
ference between the disk diameters by twice the sine. For
example, let f = taper per foot; i-S = diameter of large disk;
1.25 = diameter of small disk; and f = the required center

distance. Then -^^ --

0.03125, which is the tangent of
Sin I degree 47.4 minutes =

= 0.03123;

o-^.'i

: 4.00:

inches ^

degree 47.4 minutes.

i.^o — i.2i; = 0.2s inch;

distance c.

A practical type of taper gage, which incorporates the prin-
ciple illustrated at £ in Fig. 9, is shown in Fig. 10. This gage
is made up of two adjustable straightedges mounted on a cast-
iron body having a convenient handle on one side by which
the gage may be held or clamped when in use. The straight-

GAGING AND INSPECTION

edges are made of tool steel, hardened, ground and lapped,
and are adjusted either to a standard taper gage or by means
of disks, as previously mentioned.

Taper Pin Gage. — A standard gage for testing taper pins
is shown in Fig. ii. This gage is made so that it tests Nos.
7, 8, and 9 taper pins. It consists of two straightedges A and
B fastened to a cast-iron base C. Located close to the largest
diameter of each size of pin is a spring plunger D which Is
operated by the individual handles E for removing the pin
after gaging. Lines F and G for each number indicate the

minimum and maximum sizes at the large end of the pins.
In being tested, the pins are slid along the slot until they bear
against the sides of the straightedge. If the large end passes
the limit hnes, they are rejected.

Gage for Screw Machine Work. — In the following para-
graphs are shown a number of examples of gages from practice.
A type arm pivot made on the automatic screw machine is
illustrated in Fig. \2, and an interesting form of gage for test-
ing the accuracy of these parts is shown in Fig. 13. The thin
ends of this part constitute the main bearings of the pivot;
the tolerance allowed is very small. Referring to the illus-

■

■■■

T^^^vr«3^^^^^^i

Tig. 11. Gage tai TeEtmg Standard Taper Pins

tration of the gage shown in Fig. 13, the block A is modate the spring which returns the gage to its orig
secured to the base by means of two screws and two inal position after it has been moved back by tht
pins, and it is drilled to receive the gage B. This handle E to allow the work to be put in place. Tc
gage is a press fit in the block A. A similar block C check the dimensions of a piece of work with thL.
is secured to the base and driUed to receive the gage gage, the inspector pulls back the lever which moves
D. This block is of greater length in order to accom- the gage D with it. This enables one end of the

1 ^

i\
oj

1
®

i '!

1 "

to ^

=i=
P

GAGING AND INSPECTION

type arm pivot to be slipped into the gage B, which has a
hole in it of exactly the same shape as the end of the work
to be gaged. The handle E is then released and the spring
returns the gage D over the opposite end of the work. It
will be seen from the illustrations that the limit of tolerance
on these pins is between 0.0536 and 0.0540 inch, and the gage
indicates whether the dimensions are within these limits by
the position of the movable

!>-■

t*- 0.«6- 0.001 ~*\

gage D. All screw machine
operators do not have a mi-
crometer graduated to o.oooi
inch, and this gage takes the
place of such a micrometer
with perfect satisfaction. Holes and slots are provided at the
left-hand end of the gage for checking the dimensions of the
large diameter and the length of the work.

Pi«. 13- Gsgo for Pi

Limit Gage for Measuring Recessed Work. — The parts of
a limit gage for measuring recessed work are shown in Fig.
14, together with an assembled view of this tool and an illus-
tration showing how it is used. The plug A enters the hole
in the body of the gage B which has a dovetail slide machined
in it to receive the two gage plates C. Pins D fit in the
holes in the plates C and also extend through the elongated
holes in the cover-plate E. In using this gage, the operator
takes hold of the two pins D between his thumb and index

REFERENCE AND WORKING GAGES

finger and draws the sliding plates C back until the pins engage
the inner ends of the elongated holes in the cover-plate E. The
plug A is then pushed into the hole and causes the sliding
plates C to move out from the center. There are two shoulders
above the pilot on the plug A . In order that the work shall pass

inspection, it will be necessary for the first shoulder to enter the
hole in the gage; but if the second shoulder can also be entered
into the hole, it shows that the work is too large and results in its
rejection. After gaging, the plug A is pulled out and the pins
D drawn back so that the gage can be removed from the work.

CAGING AND INSPECTION

In making this tool, the plug A is hardened, ground and
lapped to the required size. The body B is next made with
the dovetail groove to receive the sliding plates C, which are
made in one piece to enable the hole to be lapped to size and
the piece to be placed on a mandrel to grind the outer surfaces
to the required diameter. Before hardening, the piece form-
ing the two plates C is sawed ahnost through at the center
from both sides, and after lapping the hole and grinding the
outside, the piece Is parted to form the two plates C. A gage

Simple FormE of Limit Gaees

of this type can be used to advantage in measuring a great
variety of recessed work.

Inspection Room Limit Gages. — Two interesting limit gages
are illustrated in Fig. 15. These gages are employed for in-
specting parts that are produced at the rate of several thousand
per day, and give perfect satisfaction. Both gages are built
along identical lines. They consist essentially of a plunger
P, plunger head ff, plunger barrel B, spring S, and barrel cap
A. The outer face of the cap consists of two planes accu-

REFERENCE AND WORKING GAGES

rately ground within j^j inch of each other, this being the
limit within which distances X and Y are permitted to vary.
The step or rise of s\ inch thus formed on the cap A extends
across the center of the cap end. In the upper iUustration, the
important dimension is the depth ,Y of the bevel seat from
the outer edge of the piece W. In the lower illustration, Y
is the important dimension. When A' and Y are right, the
outer end of the plunger projects as shown. When -V is too
large or Y too small, the plunger end is completely inside the
cap A, and when the reverse is the case, the plunger projects
beyond the shoulder formed on the face of the cap, The
principal advantage of these gages is that work can be carried

^-j-

—- .

^--c---^

"■"""■'-"■^

D 1

.-.-..__S

,...„,

Pig.

9 T;pc« of Limit Plug Gigai for Small Work

on with the help of cither sight or touch, and thus one sense
can be used to relieve the other — a feature that will be fully
appreciated only by those who are continually employed in
inspection work.

Making Limit Gages. — A simple form of limit gage for
testing a hole is shown at A' in Fig. i6. Manufacturing
standards for the principal dimensions of limit gages are slightly
different in various factories, but the following system will
be found satisfactory: A is always \ inch; B, 4 inches; C,
one and one-half times the diameter of the hole to be gaged;
D, ■j'j inch smaller than E and F, which, of course, are deter-
mined by the work to be inspected. The portion between the
ends is knurled, and two flats are milled on opposite sides.

GAGING AND INSPECTION

These are for the purpose of stamping the part number and
the gage sizes. Assume that the hole to be tested is g inch
and that a variation of 0.0005 '"'^^ is allowed — 0.0003 ""ch
oversize and 0.0002 inch undersize. In this case, the long end
of the gage should be 0.8748 inch, marked "go," while the short
end is 0.8753 inch, marked "not go." The two-step form of
gage is illustrated at V in Fig. 15. This arrangement is em-
ployed by many tool designers because the hole can be tested
without withdrawing the gage to insert the other end, which
is necessary when using plugs of the type shown at X. T his
gage presents one decided objection, however, as it is impos-
sible to tell what portion of the gage is bearing on the work
in cases where the hole is slightly tapered. Notwithstanding
this objection, these gages are frequently used.

The lathe work on gages is a simple operation for a tool-
room lathe hand and requires no comment, except to state
that the pieces should be recentered before hardening. The
reason for this is that heavy roughing cuts, together with the
operation of knurling, distort the centers to a certain extent,
and this is sure to cause trouble in the grinding operation.
To insure further accuracy, the centers should be lapped after
hardening to remove the fire scale.

Grinding and Lapping Gages. — There are three kinds of
materials used for wheels for gage grinding, viz., emery, corun-
dum, and artificial alumina abrasives, the last being known
to the trade as "aloxite," "alundum," etc. Genuine Naxos
emery will probably always be used to a certain extent on
very fine work, owing to the fact that it gives a high finish.
Emery wheels are comparatively slow cutting, but as gage
work is an exacting operation, the extra time spent in the
grinding operation is negligible when the best finish possible
is desired. Corundum wheels are often used for the work
in question with excellent results, as corundum is really a high-
grade emery in that it contains more alumina and less im-
purities than the best grades of emery. In selecting corundum
wheels, care must be exercised to obtain only the best quality,
as poor corundum makes a very unsatisfactory wheel. Both

emery and corundum are natural products. The artificial
alumina abrasives are faster cutting than the natural ones,
and, for this reason and because they are readily obtained
from almost any reliable mill supply house, they are exten-
sively used for work of this kind. These wheels can be run
safely at high peripheral speeds, from 6000 to 7000 feet per
minute, whereas emery and corundum wheels should never,
under any circumstances, be allowed to exceed 5500 feet per
minute surface speed.

It is impossible to state definitely the exact grit and grade
of wheel to be used for gage grinding, as the conditions vary
greatly. As a general thing, however, grits 60 to 80 and grades
K to K are used. In selecting aloxite wheels, it must be borne
in mind that their grade scale is the reverse of the ones com-
monly used. As an illustration, an alundum wheel in J grade
is quite soft, while an aloxite wheel in the same grade is several
grades harder. Full information on this point is given in
Machinery's Handbook,

Gage grinding differs but little from any cylindrical grind-
ing operation, except that extreme care must be used in sizing
the work to leave just the right amount for lapping; while
o.oooi inch is of little consequence in grinding, it often proves
a large amount to remove by lapping in cases where the work
already has a mirror-like finish. The correct amount to leave
for lapping depends upon the grit and smooth cutting qualities
of the wheel used. A 60 grit wheel will leave deeper marks
in the work than a 70 or 80 grit wheel, and a wheel that is
properly dressed leaves a smoother finish than one that has
simply been roughed up. In general, from o.cxx)2 to 0.0003
inch is sufficient allowance for lapping.

It is imperative that gages be lapped after grinding, no
matter what kind of wheel is used; otherwise the friction be-
tween the work and the gage will soon wear the latter slightly
undersize. This is because any piece of ground work (no
matter how fine a wheel has been used) always shows in-
numerable scores and high spots when examined under a micro-
scope. The high portions would soon wear away after the

86 GAGING AND INSPECTION

gage were put in use, and the object of lapping is to wear the
high spots away and bring the gage to a mirror-like finish,
which will resist wear for a comparatively long time. There
are several methods used for lapping cylindrical gages, the
most crude and unsatisfactory being to polish them with fine
emery cloth. This is poor practice, and it is never resorted
to by the toolmaker who understands his business. Another
method is to use a wooden clamp not unUke the polishing
clamps used for finishing shafting some years ago. Lard oil
and rouge are used, and good results are possible in the hands
of an expert workman, as the rouge has not enough abrasive
action to remove much more than the actual high spots. Great
care must be taken while grinding to leave just the correct

Fig. 17. Form of Lap aicd for Lapping Plug Gages

amount for lapping if this method is employed, because, after
the actual high spots are removed, the rouge cuts the finished
surface very slowly.

The most practical method is to use a cast-iron lap and
carefully washed flour emery mixed with lard oil. A lap of
this kind can be easily made as shown in Fig. 17. It consists
of any convenient piece of open-grained gray iron with a hole
bored in one end to receive the work. The extra length serves
as a handle. Laps of this kind should be split and provided
with a screw for taking up wear, as a lap should fit the piece
snugly in order to do good work. The lapping operation should
not be hurried unduly, as this procedure will sometimes result
in an undersized gage; and while there is always a chance of
saving a gage that is a tittle oversize, one that is undersize
is an absolute loss. The work should be washed in gasoline

REFERENCE AND WORKING 'GAGES

before calipering and then cooled in water that has stood in
a bucket long enough to acquire the temperature of the room
through radiation ; otherwise a very slight error will be
apparent, even though the work ihay be done by a competent
workman.

Gages made by the above methods are not absolutely accu-
rate when compared with the famous Johansson gages. How-
ever, they arc accurate enough for regular commercial work,
and as they can be made at low cost, no great expense is in-
volved when they go to the scrap box after being worn to the
point of uselessness.

Electroplating Gages. — One of the serious problems of
interchangeable manufacture is the maintenance of gages.
Obviously a gage, whether external or internal, begins to wear
with the first piece gaged, and wear is continuous with use.
The question is: what limits shall be put on gage wear which,
when exceeded, will require that they be discarded or returned
to the tool-room for readjustment? If the limits established
are very narrow, the cost of inspecting gages and restoring
them to their original condition will be very heavy; and on the
other hand, if the limits are wide, the gages will eventually
become so worn that their usefulness as a means for main-
taining standards will be lost.

The electroplating process presents a means by which gages
may be restored to their original condition at a minimum
cost. The process may be used also as a check on the wear
by which any user will be appraised of the fact that the gage
has worn below standard. Suppose a hardened steel plug gage
is electroplated with a copper film 0.00005 inch thick. The
total increase in diameter of the plug gage is then o.oooi inch.
Suppose this is established as a limit of wear of the plug gage.
Then the limit approximately is reached when the copper film
is worn through and the hardened steel becomes visible. The
restoration of the gage to the original size is merely a matter
of suspending the gage in the electroplating bath a certain
number of minutes, the time depending upon the thickness
to be deposited, the voltage, and other factors affecting the

88 GAGING AND INSPECTION

deposition of the copper. All these factors may be accurately
determined and the electroplating battery may thus be em-
ployed as an accurate means of building iip to the exact size.

The objection to this system that doubtless will be urged
is that copper is a soft material and wears rapidly, but a ikin
film of copper deposited on hardened steel wears comparatively
slowly, as experience has demonstrated. The method is one
that is worthy of the earnest attention of gage-makers, tool-
makers, and others concerned with the manufacture, use, and
maintenance of gages used in interchangeable manufacture.

Many different types of gages have been devised for test-
ing surfaces, measuring shoulder distances, and determining
the amount of eccentricity or the truth of cylindrical parts.
The ordinary plug or snap gages, while extensively used in
interchangeable manufacture, do not indicate the amount of
error that exists in the part; they simply determine whether
the parts are small or large. The solid profile gage has a
similar disadvantage in that it does not show how much the
pro&le of the part is out; and for such purposes, properly
designed indicating gages must be used.

Templet and Profile Gages. — Templet and profile gages,
which are generally made from sheet steel, are used for meas-
uring shoulder distances, profiles of irregular shape, and angles.
These gages are usually comparatively cheap to make, and in
most cases are sufficiently accurate for the work they are in-
tended to inspect. Take, for instance, the gaging of the over-
all length of a shaft as shown at A and B in Fig. i. For work
of this kind, a templet gage can be satisfactorily employed.
It should be made as shown at B, however, rather than as
shown at A. The reason for this is that there is less liability
of the operator's springing the gage by forcing the work into
it. In the type shown at B, work which will enter the "go"
end of the templet cannot be forced as easily into the "not
go" size as in the type shown at A. On the other hand, the
type shown at A, when used with care, has the advantage
that there is less liability of the operator's fitting the work
to the "not go" end, instead of to the "go" end.

Another case where a combination gage can be used with
saUsfactory results is shown at C In this case, the templet
controls the shape of the head as well as its thickness. Al-

GAGING AND mSPECTTON

though more than one point is being tested by this gage, the
worli is not usually required to be very accurate, and a templet
gage of this kind is satisfactory. Reference to this illustration
will show that the work on the "go" end should bear all over
on the gage, whereas on the "not go" end it will not go com-
pletely down into the slot. Where the thickness of the head
from a shoulder is the only point that is necessary to hold
accurate, a gage of the swinging arm type is much more satis-

factory than the templet form. This matter will be dealt
with more fully later,

A simple templet for testing work of angular shape is shown
at £> in Fig. i. In this case, the templet is used to test the
diameter of the screw and the thickness and angle of the head.
For accurate work, too many points are being tested, but for
the average run of flat-head screws, a templet gage of this type
gives satisfactory results. When greater accuracy is required

PROnLE GAGES

on work of this shape, a progressive gage covering each indi-
vidual point would be more satisfactory.

Another application of the templet system of gaging in the
production of shoulder shafts is shown at A, B, and C in Fig.
2. At .4 is shown a templet which is used for controlling the
shoulders of one end of the shaft — for the first operation;
at B is shown the gage for controlling the length of the
shoulders on the opposite end of the shaft — for the second
operation; at C is shown the gage used by the inspector for
covering the entire length of the shaft. It is much more satis-
factory to supply the workman with a gage of the type shown
at B for the second operation than it is to supply him with
the type shown at C. The latter should only be used by the
inspector, for the reason that, as long as the work goes in this
gage, it is satisfactory; if it does not go in the gage, it is un-
satisfactory. This gage is, therefore, given as wide a tolerance
as possible. For the second operation, as shown at B, the
shoulder a would be controlled by the end b of the gage. When
the length of certain shoulders is required to be accurate, this
system of inspection is not recommended, and a limit gage
(to be described later) should be employed.

A form of templet gage which is used extensively in the
manufacture of engine lathes and other similar machine tools
is shown at D. This gage is used for testing the angle on the
ways of the lathe on which the carriage operates, and at the
same time for determining if the distance between the V's is
correct. Extremely accurate results are obtained by means
of this templet gage in the hands of an experienced operator.
Either a feeler or thin piece of tissue paper is used to test both
the angle and the distance of the ways. When templet gages
of this shape are accurately made and carefully appHed, satis-
factory results are obtained.

Another application of the templet system for testing the
arc of a drcle is shown at E and F. In this case, the part being
tested is a ring for a ball thrust bearing. At E, the curve on
the lower surface is being tested with a templet; at F, two
knife-edge shaped disks are used to test the center distance

GAGING AND INSPECTION

1ST OPERATIOM

I
I

-L_.

2ND OPERATION

I
I

..— — ^

INSPECTION

I
I
I

—I

^_^

^, — -X%J

SHAPE AND LENGTH OF OOIVE

Macklnerff

Fig. 3. Various Fonns of Temiilet and Profile Gages

of the raceway. Inaccuracy of the work is indicated by light
showing between the gage and the work, but the gage does
not determine how much the work varies from the size or shape
required. For this purpose, an indicating gage should be used
in preference to the templet form.

PROFILE GAGES

An application of the templet form of gage to curve and
length measurements is shown at G. In this case, the piece
being tested is the ogive or nose end of a shell. Two points
are tested — one is the shape of the nose, and the other the
location of the "bourrelet" or the cylindrical portion on the
head end of the shell which rests in the gun and is formed by
the termination of the ogive and the beginning of the reduction
or recess on the body. In this case, the templet is so made
that it can be used in connection with the limit system of
manufacture, having two Unes on it, one indicating the mini-

Fi|. 3. Built-up Type of Profile Gage (or Shiapoel Sbells

mum and the other the maximum position of the bourrelet.
The position desired is midway between these two points.

Built-up Templet Gage. — A built-up templet or profile gage
which was made to supersede one made from /j-inch sheet
steel is shown in Fig. 3. This is used for the final inspection
on a 3-inch Russian shrapnel shell. Work which passes through
it is satisfactory, while work which will not pass through it is
rejected. The gage is provided with legs which support the
outline plates at a distance from the surface plate equal to the
radius of the shell. It consists of a base made from machine
steel, ^ inch thick, with a clearance hole of approximately
rectangular shape. Onto one side of this baseplate are screwed

GAGIKG AND DJSPECnON

and doweled four strips of hardened tool steel which form the
gage proper. It is also provided with six bumper pieces
attached to the lower side of the gage body. These bumpjers
are tapered back so as to form a bell-mouth and locate the
shell approximately as it is about to enter the gage. When
the profile of the gage wears, any one of the four strips is moved
inward, correctly placed, and then the dowel holes are re-
reamed for a slightly larger dowel-pin.

Limit System applied to the Gaging of Shoulder Distances. —
Fig. 4 shows a gaging device for inspecting shoulder shafts,
that works on the limit principle. This gage consists prind-

.--

' i ■

:::id,

— 1

'■©

'' :

...J^

- irz~

«„.,.,,!

pally of a base A carrying a V-block B in which the work is
clamped by means of a strap C and the swinging bolt D. The
relative locations of the two shoulders are determined by two
levers E and F, respectively, which carry limit buttons of the
form shown at G. These levers are fulcrumed on one side of
the gage on a pin U, and fit in slots in the hardened, ground
and lapped block /, In using this gage, the work is put into
the V-block, and the operator holds it with one hand while
he moves down lever F with the other hand until the shoulder
J on the work is in contact with the "go" limit on the plug
held in lever F. The swinging strap C is then clamp,ed by
means of the bolt D, holding the work rigidly in position. The

operator then brings down lever E and tests the location of
the second shoulder m relation to the first. In this way,
shoulder shafts can be held within very close limits when
necessary. If the limits were very close, it would be possible
for the operator to spring the "not go" surface on the plugs
past the work, but as in practically al! gaging devices the sense
of touch is necessary, there is no reason why an operator should
apply greater force when he has the leverage to do so than
is necessary to bring the measuring surfaces on the gage in
contact with the work.

Progressive or Combinatioii Gages. — Gages which are used
for inspecting a number of dimensions on one particular piece
are generally termed "combination" or "progressive" gages.

ni. 5-

ing FiUi

One type of gage which illustrates this principle is shown in
Fig. 5. In this case, the gage is used for testing the body,
over-all length, head, slot, and thread of a fillister-head screw.
The only part for which limits are provided is the thread. This
is tested in a "go" and "not go" threaded bushing inserted
in the templet. Gages of this kind have one marked disad-
vantage in that, as soon as any one position or point on the
gage becomes worn, with the exception of the threaded bush-
ings, the entire gage has to be discarded. For screws and
other parts which do not require to be extremely accurate,
however, this gage gives fairly good results and is quite ex-
tensively employed. When the work tiemands greater accu-
racy, separate gages should be provided for testing each dimen-

PROnLE GAGES 97

sion. This necessitates a more costly gage-set, but, when very
accurate work is essential, the cost of upkeep is less.

Progressive Gagii^ of Cartridge Chamber in Rifle Bairet. —
Another example which could come under the class of pro-
gressive gaging is shown in Fig. 6. This illustrates the tools
and gages used in machin'ng and inspecting the cartridge
dianiber of a rifle barrel. It is not an easy problem to produce
a perfectly chambered rifle, and it requires both a high degree
of workmanship and a complete and practical gaging system.
The chart shown in Fig. 6 illustrates the counterbore, roughing
and finishing reamers, and also the roughing and finishing gages
used for machining and gaging the chamber in a 0.303 Ross
military rifle. At first glance, it would appear that there is an
excess of gages used; however, this is not the case, as the fol-
lowing e.xpianation will show.

The manner in which these tools and gages are used is as
follows: The chamber is first roughed out with a counterbore
M and then gaged at the mouth and in the bore with the gage
A, to see that the counterbored hole is of the exact diameter
and is concentric with the bore in the barrel. (It is necessary
that this point be carefully determined, because any eccen-
tricity would be diihcult to correct in the following operations.)
The chamber is now reamed with a roughing reamer N and
gaged with the gage B. The reamer shown at Is then used
for fmish-rcaming the taper and neck and also for roughing
the cone diameter. It would be impossible to make one gage
so that it would act as a detector for all the various diameters
finished by this reamer, and tliis inspection operation requires
the use of gages C, D, E, and F, the limit lines on which should
come flush with the end of the barrel when the reamer is of the
correct size and is inserted to the proper depth.

This finishes the rough-reaming and respective gaging opera-
tions, after which every part of the chamber is again finished
with finishing reamers and gaged. The operations accom-
plished by the reamers P to T, inclusive, are inspected witii
the gages G to A', inclusive, which are made so that a slight
change in diameter can be noted by shaking the gage. The

98 GAGING AND INSPECTION

reamers U and V and the gage L are used for machining and
gaging the lead to the rifling grooves. The lead may be briefly
defined as the conical funnel which leads from the chamber
to the bore. If the chamber ended abruptly at the begimiing
of the rifling grooves in the bore of the barrel, the sharp ends of
the lands would cut strips out of the nickel jacket case of the
bullet. The lead must be concentric with the chamber and
bore, or else the bullet will be likely to wobble or "tumble"
after it leaves the muzzle. The progressive system of gaging
is necessary to obtain the desired accuracy.

Progressive Gaging of Screw Machine Products. — The two
previous examples of progressive or combination gages illus-

ifully InspBcled

Irate the ways in which it is necessary to apply the gage to the
work. When a considerable number of dimensions on the
work require gaging, and especially when the work is quite
large, it is necessary to have a large gage of the type shown
in Fig. 5, which is rather bulky to handle. On the other hand,
in gaging work like the cartridge chamber in a rifle barrel,
shown in Fig. 6, where a large number of gages are required,
it necessitates lifting up and putting down each gage once for
each barrel inspected. A method of progressive gaging which
can be applied with particularly satisfactory results to screw
machine products, such as the bicycle wheel hub shown in
Fig. 7, is illustrated diagrammatically in Fig. 8. Here the
gage consists of a large cast-iron plate, the top surface of which

sJrV

i I

IrtpTti

■1 " 'ij i I 'l '' ' " — ' — *

' '" liL

I I

I •

I I

B^^^^'x^V

PROnLE GAGES

nary plugs are fastened to the surface plate, one being made
to go into the hole and the other not to go in. For gaging
the depth of the counterbore F, the work is placed on a spring
plug, as indicated in the section of the end view of the tixture.
Here the lower face of the work rests on a swinging arm, and
in doing so forces down the spring-operated plunger. When
the work is correct, this slips over the "go" block, but will
not go over the "not go" block. For gaging the height of
the shoulder G, the work is let down into the swinging arm
instead of on a plug, and the work itself, instead of a hard-
ened plug, passes over the "go" block when correct. For
the gaging of the height H, a scheme similar to that used
for gaging the height F is adopted. For gaging the height /
and also the taper, the plug is made with a tapered shoulder
and the work rests on this taper and is guided near the bottom
only by a shoulder on the stud. In this way, the height and
diameter of the taper are controlled. For the over-all length,
the work is simply passed under limit height blocks.

The facility with which work can be handled in this manner
is remarkable. For instance, an experienced operator could
gage all the ten dimensions noted on this particular part in
from eight to ten seconds, and when the tolerances on the work
are from 0.003 to o.oog inch, this type of gaging is sufficiently
accurate. It is especially advantageous for the inspection of
work which, after being turned out on the screw machine or
turret lathe, is heat-treated and then must be finished by grind-
ing. The grinding tolerances can be provided for on this rough
inspection gage. Where a greater refinement is necessary on
the work, accurate gages can be fastened at frequent intervals
to the top surface of the plate and the gaging of the parts done
in the same way as outlined. For instance, it would be a
simple problem to attach any type of indicating gage to a plate
in this manner and thus bring all the gages for any certain
piece together, so as to eliminate the necessity of lifting the
gage to the work or moving from one place to the other along
a bench. This principle works out very successfully when the
work is comparatively tight, clean, and free from burrs.

GAGING AND INSPECTION

Id designing a gaging fixture of this type, it is desirable to
keep the work on the surface plate as much as possible. This
feature has been adopted because it is simpler to slide the
piece along the plate than it is to keep lifting it up from point
to point. Of course, there are cases where this is impossible,
but the aim in view should be to eliminate, as far as possible,
any feature which would tend to tire the inspector. Another
advantage of this type of gage is that girls can be satisfactorily
employed for the work.

Gaging the Taper on a Rifle Barrel. — After the barrel of
the Ross rifle has been finish- ground externally, the taper,

which is 0.0074 inch per inch, is inspected in the gage shown
in Fig. 9. The barrel is held in the supports A, B, and C,
which act as a stand, and also as limi t "points," snap gage D
working in between them. The limit blocks are all placed
the same distance apart — 0.688 inch — and as a greater limit
is necessary at the center of the barrel on account of spring
in grinding, the part of the gage for the muzzle end is padded
on one side to reduce the limit. The limit allowed at the
muzzle end is 0.001 inch, the padded side of the gage being
held against the "go" block A. The Umit allowed in the center

and large end of the barrel is 0.002 inch; the gage D for these
parts not being padded, it has a greater movement between
the limit blocks. The barrel is gaged at the muzzle and near
the breech end at the points where the front and rear sight
bases are located, so that the sight bases will be in the same
relative positions on each barrel.

Gaging the Bolt of a Ross Rifle. ~ After the head of the bolt
is form-milied, it is gaged in the gages shown in Fig. 10. The
gage shown at A locates the position of the faces of the lugs
by means of pins driven into the V-block in which the bolt

is placed. A point worthy of attention in this gage is the
staggered position of the J-inch pins a, shown in the plan view.
Locating the pins in this manner facilitates the inspection of
the work. The thickness of the lugs is tested by means of the
standard snap gage shown at B, and the height of the shoulder
on the bolt head is gaged in the gage shown at C. This latter
gage consists of a plain block in which the limit gage, provided
with "go" and "not go" bosses is held by a screw.

An interesting gage for taking a difficult measurement is
shown in Fig. 11. This gage is used for inspecting the width
of the spiral ribs on the bolt. It consists of a block A, to

I04

GAGING AND INSPECTION

which is held a rigid jaw B and a swinging jaw C. The limit
snap gage Z>, which is used to take the measurement, fits over
the ground ends of the jaws B and C. That part of the jaws

EXTRftCTOR

NOT 00

which comes in contact with the spiral ribs on the bolt is cut
to fit the spiral rib, which makes one turn in 4.86 inches.

Another interesting use of a so-called "rocker gage" is shown
in Fig. 12. This gage is used to gage the position of the locking
cam on the rear of the bolt head. The bolt is placed on the

PROFILE GAGES 10$

center A and the spring-actuated plug 5, and is rotated until
the cam comes in contact with the 90-degree pointed block C
The rocker is then used from the sides of the block Z), hold-
ing the center A. The pointed block C is adjusted by means
of the screw E and is set to a master bolt. The block holding
the center A is also made adjustable and is set in the desired
position.

Gaging the Extractor of a Ross Rifle. — The extractor,
which is used for removing the exploded cartridge from the
chamber in the barrel, is beveled on the back and fits in a
groove cut in the bolt sleeve. The thickness of this extractor
and the angles of inclination of its back are gaged in the block
and rocker gage shown at A in Fig. 13. The extractor is lo-
cated between four pins a, and the rocker shown at B is applied
as illustrated. The tapered sides and width of the extractor are
gaged in the block gage shown at C This gage, instead of hav-
ing a rocker, consists of a plain block beveled to the required
shape and to which four blocks are fastened, two on each end.
The blocks on one end are ground so that a perfect extractor
will not enter, while the blocks on the other end are groimd
so that a perfect extractor will enter.

CHAPTER V
INDICATING GAGES

Indicating gages may be divided into three distinct elates —
those employing the sense of touch, those depending upon
sight, and those upon hearing. These three classes are subject
to considerable subdivision, but the main principles involved
remain the same, Gages which employ the sense of touch
are known as "flush-pin" or "feeler" gages; those employing
the sense of sight are "multiplying lever" or "dial indicating
and micrometer" gages; while those depending upon the sense
of hearing produce some sound when the part is of the required
size, tension, etc. A common type of gage employing this
principle is an electric gage, in which a bell is rung if the piece
is of the right size.

Indicating Gages Employing Sense of Touch. — The most
common form of indicating gage employing the sense of touch
is the flush-pin type of gage shown in Fig. i. Reference to
this illustration will show that the gage consists of a base A
carrying a bracket B and a measuring spindle or flush-pin C.
The forward end of bracket B is machined to circular shape
and is provided on its top surface with a step equal in height
to the permissible tolerance on the work — in thb case, 0.005
inch. The lower end of spindle C is made sufficiently large
to seat on the counterbored seat in the work. The distance
from the lower face of this enlarged portion to the reduced
shoulder on the spindle is such that, when work within the
required limits is being tested, the counterbored seat in the
work will lift up the spindle sufficiently to bring the shoulder
on spindle C either flush with the upper or lower shoulder on
the boss on bracket B or midway between these points. The
most desirable condition is to have the shoulder on the fiush-
pin midway between the plus and minus limits. While 0.005

INDICATING GAGES

107

inch can be seen with the naked eye, it can be detected more
rapidly with the finger, so that this type of gage is known as
the "flush-pin" or "touch-type" of gage. The sense of touch
is much more accurate than most people appreciate, and, as
a matter of fact, it is possible to detect differences as small
as 0.0003 inch.

MAPHRAOM I r '~C

r j. J^ "^ MAX. 0.40»''
I ^--'''"' "■'•-^-.^ I MIN. 0.400"
U ""^ . , ""-■■J — .

~^M —
I' I

. . Ill ll

TTfT

II, II

MwMmvrji

Fig. X. Simple Indicatiiig Gage of Flush-idn Tsrpa

Another type of gage which depends for its accuracy upon
the sense of touch is shown in Fig. 2. This gage is used for
testing the position of the milled groove on the imder side of
a bolt sleeve for a military rifle. The sleeve proper is held
in a fixture on hardened and ground plugs i4. By and C. Plug

INDICATING GAGES

109

the work. This gage is also used for testing the height of the
shoulder / on the bolt sleeve, the rocker H being located on
the hardened and ground block 7 in a manner similar to that ,
previously described. In applying this rocker, it is laid on the
hardened and ground surfaces of the fixture and then moved
forward to see if it will pass over the work. The "go" end
passes over the work and the "not go" does not, if the work
is satisfactory.

A flush-pin gage which is used for determining the depth of
a slot in a rifle part is shown in Fig. 3. In this case, the slot

//sa //7

'^"'"^^ j

Fig. 3. Fltuli-pin Tjrpe ot Gage emiloring a Swinging Arm

j4 in the part is inspected by two flush-pins B and C which
are held in a swinging member D in the bracket E. Swinging
member D carries a hardened and ground locating plug F
which, when in position for gaging, comes in contact with a
hardened and ground plug G in the base of the gage. These
two pins insure that the swinging member is always brought
to the same position. Then, by feeling the height of the flush-
pins in the swinging member, the depth of the slot is tested;

GAGING AND INSPECTION

the piece being gaged is held on the base of the gage on dowel-
pins, and is ejected after being tested by means of handle H
. tlirough an eccentric movement.

Indicating Sight Gages. — Indicating gages employing the
sense of sight may be roughly divided into five general classes,
viz., those of the multiplying lever type; those of the needle
and dial indicating tyi>c; those employing a micrometer screw;
those using the cross-hair microscope in connection with the
micrometer screw; and those employing the reflection of light
rays.

Multiplying Lever Type of Gage. — The average gage con-
structed on the multiplying lever principle, when used for fine
measurements, has several disadvantages, chief among wliich
is the weight of the moving parts. This can be largely compen-
sated for, however, by the correct proportioning and arrange-
ment of the levers, so as to balance the weight of the various
parts. When set by a master and used simply as a means of
comparison, the multiplying lever indicating gage may be
satisfactorily employed on a large range of work.

Needle and Dial Gage. — ■ Needle and dial indicating gages
are made in several different types, the type employing a train
of gears for obtaining the multiplying movements of the needle
being the most common. There are several objections to this
form of indicator, wliich may be summarized as follows: i.
Backlash in the gears due to wear. s. Fluctuation of the
indicating needle. 3. Lack of brake or dashpot to eliminate
fluctuation of the needle. 4. Unequal wear of moving parts —
especially of the gears.

As a rule, a gage of this type is used on one size of work for
weeks at a time, with the result that those portions of the
gears constantly in mesh wear much more rapidly than the
remaining or unused portions. This makes the gage inaccu-
rate for anything but comparative measurements, and it must
be corrected and set frequently by means of master blocks.
The fluctuation of the indicating needle is one of the most
annoying features of this type of gage. It is due to the un-
balanced action of the i»arts and to backlash in the gears.

INDICATING GAGES

For rapid inspection, a gage in which the needle continually
fluctuates is of little or no value, and It has been suggested
by inspectors that a brake or dashpot be provided in order
to eliminate this objectionable feature. The computing scale
is a good example of a measuring instrunient employing a
dashpot. and a similar arrangement adapted to an indicating
gage of the needle type would greatly increase its usefulness.
Unequal wear of the moving parts is also a factor which should
receive careful consideration. The number of parts employed
in a gage of this type should be reduced to a minimum, so as
not only to simplify its construction, but also to decrease the
chances for wear and consequent inaccuracy. As will be ex-
plained later, other types of needle indicating gages have been
devised to which the objections mentioned do not apply.

Micromckr Gages. — The micrometer caliper is a type of
gage which depends both upon sight and touch for its accuracy.
The micrometer screw has been applied to many different
types of gages, and, as will be subsequently described, this
type of gage has certain advantages for work which cannot
be measured by any other means, or which is inaccessible to
a regular snap or plug gage. The micrometer screw furnishes
an accurate means of inspecting work, but it is necessary that
a gage of this type be frequently checked with a reference gage
to see that the screw is not worn and that the measuring points
of the gage are parallel with each other.

Microscope Ga^es. — The cross-hair microscope in connec-
tion with the micrometer screw provides one of the most accu-
rate methods of insfiecting small articles, such as thread gages,
ball races, fly-cutters, etc. The number of industries, however,
employing this instrument is not nearly as great as its adapt-
ability would seem to warrant. For many classes of work,
the accuracy which can be obtained by this method is much
greater than that which would ordinarily be required,

Reflection of Li^ht Rays. — For extremely accurate work,
gages employing the reflection of light rays have been develojied.
These, however, are not extensively used and have only been
adopted where extreme accuracy is necessary and where a large

112 GAGING AXD INSPECTION

number of parts must be inspected in a certain time. The
light ray presents a rapid means of ascertaining inaccuracies
as small as o.oooi inch, which can be read off from a screen
with great rapidity. For such work, a highly developed in-
spection and gaging system is necessary.

Multiplying Lever Indicating Gage. — Multiplymg lever in-
dicating gages are made in so many types that it is impossible

INDICATING GAGES

holder B is free to slide. A stud C in the rear end of the base
acts as a pivot for the swinging arm D, the latter carrying the
indicating needle E and plunger F. The fulcrum point of
pointer £ is so placed in relation to the knife-edge which comes
in contact with plunger F that a multiplying movement of
25 to I is obtained. To insert the work under the measuring
plunger, arm D is raised, its movement being stopped by the
fillister-head screw C.

There are several objections to this gage. In the first place,
the necessity of raising arm D to insert the work makes it
possible for dirt to collect under the seat, and thus cause the
gage to read incorrectly. It is also unsuited for very accurate

"" - . ' '^ ' I:' :. ... J 1ml

Fie. S. Multiplying Lavei Icdluting Gage for Internal Work

work, because of the small multipljing movement of the lever,
which gives only 0025 inch between each graduation on the
scale for each 0.001 inch variation in the work.

Multiplying Lever Gage for Internal Work. — Another multi-
plying lever indicating gage, which is used for measuring in-
ternal work and is provided with two multiplying levers, is
shown in Fig. 5. Reference to this illustration will show that
the gage consists of a sleeve A , inside of which is fitted a member
B milled out to receive the two multiplying levers C and D.
The gage is provided with three contact points, only one of
which — point E — is movable, the other two being adjustably
held in the sleeve A . A coil spring, as shown, keeps the forward
end of lever C in contact with the lower end of contact point
E and another spring keeps the forward end of lever D in con-

TI4

GAGING AND INSPECTION

tact with the rear end of lever C. In this way, the point fi
constantly follows any irregularities in the work, and these
are indicated on the dial F. On the exterior of sleeve ^ is a
bushing C, which can be moved baclt and forth. The function
of this bushing is to keep the axis of the gage, as nearly as pos-
sible, parallel with the
center of the work, the
sleeve being pushed
back and forth, depend-
ing upon the distance
from the face of the
work that the measure-
ment is taken.

There are several ob-
jections to this gage:
One is the small multi-
plying movement which
be obtained;
another is the unbal-
anced weight of the
moving parts. In a
gage built on the mul-
tiplying lever principle,
the multiplication should
not be less than 60 to
1 to 1 being pref-
erable. This provides
for a movement of the
indicating needle of a
minimum of approximately -,'g inch for each 0,001 inch variation
in the work. In the case of a multiplication of 100 to i, the
space between each graduation, representing variations in the
work of o.ooi inch, would be o.ioo inch, which is still better.

Simple Type of Multiplying Lever Indicating Gage. — A
multiplying lever indicating gage which can be used for accu-
rate work is shown by the diagram, Fig. 6. This gage comprises
two levers, which provide for a multiplying movement of 240

ilLnE Principle of
e employing Two
Rack TooUi

INDICATINO GAGES

115

to 1; that is, variations in tiie work of 0,001 inch would cause
a movement of 0.240 inch of the upper end of needle A. Seg-
ment B is, therefore, provided with graduations 0.024 inch
apart, each space being equal to a variation of 0.0C01 inch in
the work. The connection between levers A and C is by means
of a rack tooth, and lever
A is counterweighted, as
shown at D, making a
spring unnecessary. One
objectionable feature of
this gage is the relation
of the lower surface of
the upper or movable
anvil to the center line
of lever C. For accurate
readings, the measuring
point should be in line
with the axis A* V. As
this gage, however, is
only used for compara-
tive measurements, and
set by a master, this ob-
jection does not seriously
affect its other advan-
tages, which are simplic-
ity of construction and
great magnification.

The Hlrth Minimeter.
— A multiplying lever
indicating gage which
comprises some very val-
uable features from the
standpoint of both accu-
racy and construction is

shown in Figs. 7 and 8. This gage, known as the Hirth minmieter,
is used extensively by various concerns, and can be adapted to
almost any class of work by simply arranging suitable stands for

GAGING AND INSPECTION

holding the measuring gage proper. Fig. 8 shows a sectional
view through this gage, illustrating its working mechanism. The
sensitive action of this gage depends upon the introduction

irrorcATiNG gages

of a long lever ami A, which also serves as an indicating needle,
and a short arm, the length of which is determined by the dis-
tance between the two knife-edges B and C. The bearing
points of these knife-edges may be varied in order to provide
adjustment for the apparatus. One of the advantages of this
device is that it eliminates the necessity for lubrication and
overcomes Ihe disadvantage of play on dead centers. A light
spring D holds the lever against the knife-edge and returns
it to its normal posirion after measuring. A finger or pin £,
bearing against the lower knife-edge, makes contact with the
work to be measured. Movement of this pin causes the pointer
A to swing over the scale F, due to the displacement of one
knife-edge in relation to the other. The arc is graduated in
different minimeters to give readings to o.oor or o.oooi inch.
The entire mechanism is enclosed in a tube and the upper
part is provided with an opening which permits the graduated
scale to be seen and the indications of the pointer to be read
off. The measuring instrument proper can be mounted in
different holders.

Principles of Dial Indicating; Gages. - The chief difference
between a dial indicating gage and a multiplying lever indi-
cating gage is the substitution of a graduated dial for a gradu-
ated segment, and the provision for making the needle travel
one or more times around the dial, instead of Just covering
the segment of a circle. The dial is usually graduated so as
to give readings to o.ooi or o.oooi inch. In the dial indi-
cating type of gage, some means must -be provided for giving
one or more rotations to the indicating needle, and for this
purpose gears are generally employed. In the multiplying
lever indicating type, no gears are necessary, as the pointer
moves over an arc of a circle only and does not make a com-
plete revolution. For the average run of work, especially in
the inspection department, the multiplying lever indicating
gage, when correctly designed, is superior to the dial type.
For instance, the type shown in Figs. 7 and 8 has been found
to be a most accurate indicating instrument for inspection
use. In the following, a description will be given of some of

Ii8 GAOraG AND INSPECTION

the principal gages made on the indicating needle and dial
principle.

The Ames Dial Indicator. — In Fig. 9 is shown an Ames
dial indicator attached to a simple holder and used for meas-
uring the' depth of the powder groove in a ring for a combi-
nation time and percussion fuse. The holder consists dmply

Fig. 9. Ames Dili lodicBloi

Deptb G«ge

of a cast-iron block machined on the bottom and top surfaces
and carrying a hardened and ground plug, which supports
the fuse ring being measured. The bracket forming an inte-
gral part with this block is machined to receive the ^indle
of an Ames dial indicator. As has been previously mentioned,
a dial indicator should not be depended upon when used on one

INDICATING GAGES

119

job for any length of lime; it is always advisable to provide
a setting block, as shown in the illustration at A, to check
the instrument periodically. A spring keeps the measuring
pointer in contact with the work; the pointer is lifted by means
of lever B.

Dial Indicators employing a Train of Gears. — ^The internal
mechanism of a dial indicator which is operated by a train of
gears is illustrated in Fig. 10; it consists of a spindle A which
works in hardened and lapped bushings inserted in the case

Fig.

containing the measuring mechanism The mexsunng spindle
A b moved up and down by means of a handk B to which it
is connected by link C and collar D When spmdle 1 is raised
the rack teeth cut in it mesh with a pinion E, which transmits
motion to the gear F. pinion G, and needle H. Gear / is inter-
posed to reduce the backlash. The dial is divided into one
hundred equal spaces, and each graduation corresponds to a
movement of the spindle uf o.oor inch. The table J is adjust-
able, and a plate A' for holding the work to be measured is

3 GAGING AND INSPECTION

attached to it by screws. The stud on which table J is held
is screwed into a babbitt bushing L, the latter being clamped
to the stud by the screw M, the babbitt being poured in after
the stud is put in place.

Another type of dial indicator which has a greater multi-
plying movement than that shown in Fig. lo is illustrated in
Fig. II, This gage is used for measuring such work as bal-
ance staffs, pinions, etc., for watches. It is provided with a
dial having two hundred graduations laid off on its face. The

Dial Gage of the Caliper Type

work to be measured is placed between the Jaws A and B,
which are separated by forcing in rod C to which jaw B is
attached. Held on this rod by a screw is a rack D, which
meshes with a pinion E having forty teeth. Pinion E is con-
nected to segment gear F (the whole number of teeth in which
should be 235), which meshes with pinion G attached to needle
/. Jaw B, which b held by a screw to rod C, has a slot cut
in its rear end which fits a flattened stud E, thus preventing
the jaw from tilting. One complete revolution of needle J
around the dial gives a corresponding movement between the
jaws A and B of 0.080 incli, so that the space between each

INDICATING GAGES

s /

^^x

// \

^£^ 1

^^S\ \ 1

1 \ 1

Pr\ /

llf"

rr-?Ar pJ

Ffi- »• DUl TBit Indicator ^flni SwdiiiK to o.oooi Incb

graduation of the dial represents a movement of the jaw of
0.0004 inch. The working mechanism of the gage is enclosed
in a case and supported on a stand /, only partially shown.

A still more sensitive dial indicating gage or comparator is
shown in Fig. 12. This gage also employs the pinion and gear

122 GAGING AND INSPECTinV

feature, and is so arranged that one revolution of the needie
around the dial represents a movement of the anvil or meas-
uring spindle of o.oio inch; as the dial is divided into one
hundred equal spaces, this means that the space between each
graduation is equal, theoretically, to a o.oooi-inch movement
of the anvil. In a commercial gage, however, the movement
of the needle varies somewhat over different parts of the dial.
The working parts consist of a lever A, fulcrum screw B,

nit^S

^^^1

^ — "^-1- — 1.'.'.

aispj

(§X[J^_i__-,— =dtii

}/ '

»ar»l™«-, 1

FJE- 13. Lowe Dial Test Indjcttor

plunger D, fan gear E, and pinion G. The gage operates as
follows: When brought in contact with the work, plunger D
is moved and the flange on this plunger moves the short end of
lever A with which it is kept in contact by the action of spring
J on the segment gear and the spiral spring on the plunger.
In this way, a uniform contact is maintained between the long
end of lever A and the pin C, and also between the flange of
the plunger and the short end of lever A. The movement
of lever A causes the required movement of the segment gear,
which turns the pinion and the pointer.

mDrCATING GAGES

Dial Indicator with Wona for Rotating Needle. — An indi-
cating gage of the dial type in which a train of gears is dis-
pensed with is shown in Fig. 13. This indicator employs a
worm in place of a train uf gears for conveying the rotary
movement to the indicating needle. As shown in the illus-
tration, this gage consists principally of a body A milled out
on one side to receive the indicating lever B, which is attached,
as shown in the sectional view, to the forward end of body A .
The forward end of this lever is provided with a friction joint,
which allows the contact point to be moved around through

180 degrees to any required position, thus greatly increasing
the usefulness of the instrument. The rear end of lever B is
provided with a projection fitting in the groove in worm C
This worm is held in somewhat the same way as a staff in a
watch, and on its extreme upper end it carries an indicating
needle D. The needle is retained at zero by means of the
flat spring E and a hairspring F. The dial G is divided into
twenty-five equal parts, the distance between each graduation
representing a movement of the lever B of 0,001 inch. The
dial is so arranged that it can be turned around to bring the
zero point in line with the needle when the latter is at rest.

GAGING AND INSPECTION

I In this instruinent the objectionable feature of backlash is
avoided, and it has been found both reliable and sensitive.
A plate, not shown, covers the internal mechanism by fitting
in a dovetail groove in the side of the body and is held in place
by a screw. By the addition of several anns, etc., this device

I can be used for various purposes.

Dial Indicator of the Caliper Tjrpe. — Another dial indicating
gage which does not depend for its magnifying movement upon
a train of gears is shown in Fig. 14. In this gage, the hand A,
which travels around the dial, is operated by means of a fusee

I chain that is wound around the spindle to which the hand is

[±1

M.,™Ft.l«!.T0OL.Tti;L

-.,.»»«,.o. 1

tan:L ©

^^^irnr-

■"PU

^F^

fastened; the chain is connected to the movable jaw lever B.
A hairspring, not shown, surrounds the lower end of the spindle
to which the hand is attached in such a way as to pull the in-
dicator hand toward zero and keep the chain wound up as far as
the caliper jaw will permit. The jaws arc separated by pushing
the button C to the right, which operates the long lever B at-
tached to the movable jaw.

Micrometer Indicating Gages. — An indicating gage which is
capable of wide application is the micrometer type of gage. This
generally consists of a micrometer spindle held in a suitable
frame, which latter, as a rule, also supports the work and enables

nroiCATING GAGES

toeasurcments to be taken at several points when desired. A
simple application of the micrometer type of gage is shown in
Fig. 15; this 16 used for measuring the diameter of a military
rifle bolt at the root of the spiral ribs. It consists principally
of a frame A holding a split sleeve B and a micrometer spindle
C. The sleeve B is held on a conical plug D by a nut and is
split so that it can be made to fit snugly in the hole in the bolt.
To lay off the manufacturing limits on the gage, the master
plug £ is placed on sleeve B, and the measuring point F is brought

Ibl contact with it. This master plug E is also used for checking
the gage at frequent intervals.

Another interesting type of micrometer indicating gage is
shown in Fig. 16. This is used for testing the location of the
llide in a receiver for a military rifle. The receiver is held in
( gaging fixture, being located by plugs fitting in both ends.
; upper surface of the fixture is provided with hardened and
round parallel strips, on which the micrometer gage is located,
f shown. The gage consists of a base A provided with a lug

which fits against the hardened and ground measuring blocks
on the stand. A cone-pointed and threaded spindle B extends
downward through the center of the body of the gage and ac-
tuates a measuruig finger C', This finger is held by means of a
flat spring ZJ, shown in the lower view, which fits in the slot in
the finger and also in the base of the gage. A cap E is fastened
to the stem of the gage by two screws, as shown, to prevent the
finger C from dropping out. The spindle B is provided with
forty threads per inch and is pinned to a thimble F. The gradu-

ij^PG 02232 !* ,
J A INSP.-0.226'

d;G

SECTION OF^l

■',l:_;.'i:

ations on this thimble are laid out after the gage has been as-
sembled and set by means of a master.

A somewhat similar micrometer gage is shown in Fig. 17.
This gage is used tor testing the distance from the center of the
receiver to the bottom of the bolt sleeve guide slots on a military
rifle. A stand similar to that used with the gage shown in Fig.
16 is used with this gage for holding the work; this gage is of
practically the same construction as that shown in Fig. 16, ex-
cept that the spindle is provided with a head which acts as a
measuring point. A standard reference block is provided for
use in setting the spindle when it becomes worn or inaccurate.

INDICATING GAGES

127

There are, of course, many other applications of the micrometer
spindle to accurate gaging, but the examples given here show
the principles involved, which are subject to considerable modi-
fication for different uses.

Three-point Indicating Gages. — In machining work which is
eccentric or unbalanced, considerable difficulty is sometimes ex-
perienced in producing a truly cylindrical hole or bearing, due
to play in the machine bearings or other causes. When the

DIAL INDICATOR

ifaeMnery

Fig. x8. Three-point Dial Indicating Device for Testing Crankshaft

Bearings

forces opposed to each other are so unbalanced that a three-
cornered effect is produced, the ordinary two-point measuring
instrument will not detect the error that exists. The only way
of successfully measuring the work to find whether it is truly
cylindrical or not is to employ a three-point measuring instru-
ment. Several devices have been made for this purpose, one of
which is the ordinary micrometer provided with a special two-
point anvil, the third point being formed by the spindle of the
micrometer.

138

GAGING AXD INSPECTION

Another device, which employs a dial indicator, is shown in
Fig. i8. This is used for measuring the cratikpins of automo-
bile crankshafts and, as shown in the illustration, consists prin-
cipally of two blocks A and B, hinged at the point C. The
upper block B is machined on one end to receive the spindle of
the dial indicator, which is held in place by means of the screw D.
When used, the indicator is swung open, slipped over the work
and then brought down in contact with it, so that the spindle
rests on the upper surface of block A, It is then possible to tell
whether the bearing is out of round or of the correct diameter.
The gage is set to the zero point by means of a master plug made
to the same diameter as the crankpin.

The three-point indicator illustrated in Fig. i8 has one disad-
vantage in that it is comparatively slow to operate and is rather

bulky to handle. An improvement over this device, which has
three points located 30 degrees apart, is shown in Fig. 19. This
device is also used for testing the crankpin bearings of a crank-
shaft and is so constructed that it can be used very rapidly.
In fact, it can be applied to the work while the latter is in motion.
It comprises a main holder A formed at the forward end to the
shape shown, and carrying two hardened, ground and lapped
. blocks. The rear end of the holder is provided with a hook to
facilitate gripping in the hand. The dial indicator, as illustrated,
is fastened to this holder. A spindle B passing through two
bearing supports in the holder proper comes in contact with the
spindle of the indicator. When in use, this instrument is set to
the desired diameter by means of a master, and ran then be
applied directly to the work while the latter is in motion and the

.^^i

INDICATING GAGES

I2Q

reading taken off on the dial indicator. For many classes of
work, this type of instrument will be found to be much superior
to the micrometer caliper, in that it is quicker to operate and
can be used in connection with the limit system of manufacture.
Three-point Indicators for Internal Work. — The indicating
devices shown in Figs. i8 and 19 are used for externa! r

Us. 10. Hirth Hinimeter fltted up for Use t» *a tntem*! Gage

ments. Fig. ao shows a device which can be used for internal
work. By the addition of a simple attachment, the Hirth minim-
eter, which has previously been described, is here used for in-
ternal gaging. The special holder is fitted around the body of
the lower portion of the indicator, and carries one adjustable
and two rigid points, the former being connected by means of
3 lever to the spindle of the indicating lever. Fastened to the
bracket of this attachment are three rollers against which the

I30

GAGING AND INSPECTION

work is pressed, and which keep it straight while it is being tested.
The two rigid points are adjustable for wear, and all three
points are provided with ball points. With this device it is pos-
able to tell if the hole is of the correct size, or if it is out of
round, tapered, etc.

Gas Engine Cylinder Gage. — A three-point dial indicating
gage designed particularly for tc-iting the bore of automobile

a Eaiiiie Cylinder Cage

cylinders is shown in Fig. 21. The illustration shows the ga^
inserted in the standard ring which is used for setting the needle
at zero. This ring has a diameter equal to that of the cylinder
it is desired to test. The base, holding an Ames dial indicator,
forms two points, B and C, and the plunger of the indicator
forms the third point A. With this device, it is possible to tell
whether the cylinder is large or small, out of round, or tapered.

INDICATING GAGES

131

Another three-point gas engine cylinder gage of simple con-
struction is shown in Fig. 22. This gage comprises a standard
dial test indicator, which is attached to a frame by a thumb-nut,
as shown. In this frame, which is made of cast iron, are set
three buttons A , two on one side and one on the other, giving a
three-point bearing. The bearing points are set 120 degrees
apart, and two of the op-
posite points and the
plunger of the dial gage
are set in the same plane,
the third being set lower
a distance equal to about
one-third of the cylinder
diameter. The dial gage
is providejd with a slip
ring, so that the pointer
may be set to zero no
matter what its position
may be. In using this
instnunent, it is pushed
into the cylinder, dial
first, from the head or
compression end, assum-
ing that the cylinder head
is detachable. Then, with
the aid of an electric flash
light, the operator or in-
spector may easily watch the variations in the cylinder diam-
eter. The instrument should be pushed through the cylinder
slowly, care being taken to have all three comers bearing on
the cylinder bore. If it is desired to use this instrument as
a micrometer, it can be set by a standard ring.

Star Gages. — A type of gage which was developed especially
to meet the demand for a convenient and accurate instrument for
gaging the bores and jackets of guns of all sizes, from the one-
pounder rapid-fire gun up to the largest caliber, is shown in Fig.
23. This gage consists principally of a body A^ in which three

Fig. aa. Gas Engine Cylinder Gage haying
a Three-point Bearing on Its Base

INDICATING GAGES

133

measuring heads are held (four can be used if desired); these
heads are radially adjustable, having tapped holes in the outer
end to which various measuring points of any suitable length
can be attached. The radial adjustment of the points is con-
trolled by a central wedge or cone, which may be moved lon^-
tudinally, and the heads are fittedso that they may rotate freely
when gaging the rifling of a gun, or may be locked for regular
work. The body of the gage is made of seamless drawn steel
tubing, provided with means for readily coupling and uncoupling
to produce any desired length. The tubular body A is graduated
throughout its entire length in quarter inches. This is essential
when it is desired to make a record of the condition of the bore
by taking measurements at regular intervals.

The operating head shown to the left is made with a sliding
member connected to the jointed rod by which the wedge in the
measiu'ing head is given its longitudinal movement. The oper-
ating lever shown is pro\-ided to give the necessary delicacy of
movement, and also facilitates the operation of the gage. The
scale and vernier shown at B enables the variations from the
required diameter of bore to be read at a glance. For each
diameter of bore to be gaged, a standard ring is usually furnished
for setting the gage. Suitable supports hold the standard ring
concentric with the measuring head when the points are brought
in contact with it, and then the vernier is adjusted so that the
zero lines coincide. For the smaller gages, the vernier gives
readings to 0.0005 iich, and to o.ooi inch on the larger sizes.

When gaging bores of considerable length, it is necessary to
support the gage and to keep it from sagging, which would
introduce a small error in measurement. Therefore, supports
such as shown in Fig. 24 are used, These are set in the bore of
the gun being measured and the gage is slipped through the
hole A . The legs of the supports are then adjusted so that the
gage is held central with the bore of the gun. A centering
device, as shown in Fig. 35, is also provided when desired.
This consists of a central hub with three graduated radial arms,
upon which are mounted .sliding jaws that project into the bore;
one of the jaws is provided with a screw adjustment for binding

134 GAGING AND TNSPECTTON'

the device in the bore. The central hub has a slot at the top
to receive the gage tube which rests on two rollers, permitting
the gage to move freely without danger of marring the surface
of the tube,

Application of Indicating Gages. — Gages of the indicating
t>pe are gradually superseding solid gages on many classes of
work, because of their greater sensitiveness. For instance, they
are used for testing external and internal cylindrical work,
parallelism of shafts, relation of angular surfaces, height and

depth of shoulders and holes, concentricity of parts, cam shapes,
strength of springs, etc. In the preceding pages, examples have
been shown of the types of indicating gages used for cylindrical
external and internal work; in the following, attention will be
given to other applications, including gages used for testing
balls and ball bearings, and the use of box-tj-pe inspection fix-
tures for work having a number of holes that must bear a cer-
tain relation to each other.

Testing Parallelism of Shafts. — For testing the parallelism of
shafts, the indicating gage is very satisfactory. One means of

INDICATING GAGES

135

determining if a shaft lies in a plane parallel with the base of a
machine is illustrated in Fig. 26. In this case it is desired to
determine whether or not the needle bar lies in a plane parallel
with the base of a sewing machine. The gage consists of a steel
base A resting on four feet C, which, as shown, come in contact
with the top surface of the table. These feet are hardened,
ground and lapped in the same plane. The hardened tool steel
plungers B which come in contact with the needle bar are flat

Fig. 25. Centering Device used with Pratt & Whitney Star Gages

on one end and spherical on the other. These plungers fit loosely
in the bearings E and are held from dropping out by adjusting
nuts F. Fulcrumed on studs G are the pointers Z), which have
hardened projecting arms that are in contact with the upper end
of plungers B, The sheet steel frame // is bent at right angles
along the bottom and screwed to the base. Right- and left-
hand coil springs L act in opposition to the plungers so that they
turn the pointers to the extreme outer position, when the gage is
not in use. When the pointers are to be adjusted, the instrument

136 GAGING AND INSPECTION

is set on parallels, and a height gage inserted under each plunger
successively, the plungers B being adjusted so as to bring the
pointers to zero. On this particular gage a limit of ±o.c»5 inch
is provided.

Testing Relation of Surfaces at Right Angles. — Many dif-
ferent indicating devices have been constructed for testing the

Fis. 16. Indicating Gaga tor Ta«Hii( ParaUalitm of Shaft

relative positions of angular surfaces, and in Fig. 27 is shown a
simple gage for detennining if the base of a gas engine cylinder
casting is square or at right angles with the bore. This gage
consists of a base A , frame B, pivot C, and indicating lever D.
The body of the gage is made in two parts to facilitate machining.

INDICATING GAGES

The indicating lever support is fastened to the body with screws
and dowel-pins, and extends into the cylinder so that the center
of the lever pivot is somewhat below the face of the flange of the
casting. By placing the gage on the cylinder flange and bring-
ing the knife-edges a and b on the lever into contact with the
cyEnder wall, any variation is shown by the mark at the upper
end of the gage. This can be so laid out that plus or minus

limits can be provided. The reason for placing the pivot below
the cylinder flange is to have it take the thrust when the indicator
is moved against the side of the cylinder bore. A spring above
the pivot holds knife-edges a and b in contact with the cylin-
der wall. The gage is simple in construction and operation.

Indicating Height and Depth Gages. — For determining the
relative heights of two shoulders, a height or depth gage is
necessary. Gages of the multiplying lever or dial indicating

^i& GAGING AND INSPECTION

type are best adapted for this purpose. Fig. 28 shows a height
gage constructed on the muItipljTng lever principle. It consists
of a base D having two shafts E fastened to it. connected at the
top by a link. On these shafts is a sliding member G, which can
be locked securely in any position by screw H, acting upon two
clamping bolts, thus obviating springing of the gage when in
use. The adjusting nut C oi>erates part /, which is carefully
fitted in the slot. On the same part is a shoulder J to which the

^@:k@)

Pig. iS. Indicitiog Heigbt Gage tot Tool-room Um

arm A is fastened. This arm is made from tubing and is similar
in shape to opening K. It is made a tight fit on the holder at J,
and a pin put through to fasten it securely. The oblong tube
A is now cut along the line ZZ, and inside of it are placed the
levers which are arranged to give readings to one-half thousandth
inch. While this gage has many admirable features from the
point of view of accuracy, it is only suitable for tool-room use,
and not for manufacturing or inspection purposes. It is evident
that a gage designed for inspecting any particular piece should
be so made that universal adjustment is not possible. In other

INDICATING GAGES

^--""^^^

^^ ^»...

...XX

^^T^^y

m
^

Tyi

-y

.^.

L_ *•

"I 1

5> ^

kmh

r.j

\\ ' i J *

ir«ttatr*

14° GAGING AND INSPECTION

words, its range should be limited to the particular work for
which it is designed.

Indicatmg Gage for Testrng Shrapnel Shells. — An indicating
gage which fulfills two functions — gaging the over-all length as
well as the thickness of the base of shrapnel shells — is shown h
Fig. 39. This gage comprises a base A in which three pins are
driven to center the shell; an upright B for supporting the in-
dicating mechanism; and attached to the top of upright B, an
indicating lever support C, which is so mounted that it is free
to swing in an arc. The device for indicating the thickness of
the base of the shell consists of a rod D that has a hardened and

ground tool steel point E and a limit pin F. A boss formed on
bracket C is provided with a step, the height of which b 0,020
inch, or the manufacturing limit allowed on the thickness of the
base. The limit pin F, when brought around, must come with
its indicating surface between the top and bottom of this step.
The desired thickness is indicated when the lowest surface of
limit pin F is located cquidistantly between the high and low
points on the limit step. To insert the shell in the gage, it is
necessary that rod D be removed from bracket C

The indicating device for the over-all length consists of'^^Hil
multiplying lever G, pivoted to bracket C at the point B, and ^

INDICATING GAGES

141

attached by a pin to plunger /. Plunger / is hardened and

ground on its lower surface and makes contact with the end of
the shell. The reading is obtained from the segment J, which
indicates the Umits on the work. This fixture is free from springs
and is of simple construction.

Indicating Thickness Gages. — The simplest form of indi-
cating thickness gage is the micrometer caliper, but as this type
of gage is well known, it will not be described here. Another
simple form of indicating thickness gage is shown in Fig. 30.
This is designed especially for gaging the thickness of the wall
of cartridge cases near the head end. It consists principally of
two caliper jaws A and B, which are made long enough to reach
down into the case, a handle C for holding the gage, indicating
pointer D, and graduated arc E. A combination locating stop
and support F is also provided to keep the jaws in alignment
with each other, and locate their measuring points at the desired
distance from the open end of the case. When in use, the jaws
of this gage are slipped over the walls of the case, and readings
taken at various points around the circumference. It is tested
from time to time by the setting block G.

Another indicating thidiness gage which is used for the same
purpose as that illustrated in Fig. 30 is shown in Fig. 31. As
this illustration shows, this gage is of the stand type, and supports
the cartridge case being inspected by means of a horseshoe sup-
port A held on upright B. Two other posts C and D carry the
gaging points, one of which, E, is held rigidly in post C, while
point F is free to slide and is kept out by means of spring C.
The upper end of post D is notched to form a limit step, and
plunger F is provided with a line which must come between the
two steps when the wall is of the correct thickness. A height
gage H is also provided which enables the thickness of the head
to be checked at the same time that the wall is inspected.

An indicating gage for testing the thickness of the walls of
shrapnel shells at a point slightly above the powder jjocket
where the inner wall is straight, is shown in Fig. 32, This con-
sists of a sheet-steel frame A carrjing a bushing B which fits
in the nose of the shell, a roller support C for keeping the gage

GAGING AND INSPECTION

INDICATING GAGES 143

I line with the axis of the shell, and two measuring points D
and E. Measuring point D consists of a hardened, ground and
lapped block, which is riveted to the frame A; point £ is a
roller attached to a multiplying lever F. Lever F swings over a
marked segment G which indicates the limits on the work, and
a flat spring 11 keeps roller E in contact with the work. In
using this gage, the member / is inserted in the shell and located
by bushing B. The gage is gripped by the handle and moved
around the circumference of the shell to test its thickness at
various points. Block J is used to test the gage for wear.

1 f^

Cin^ ^

l^i^^^^9H

^B ^^^

^mZ

mcentricity Gages. — There are several methods of deter-
ing whether or not a hole and an exterior surface are con-
centric with each other. The simplest way is to use a gage of
the type shown in Fig. 33. This is not an indicating gage, but
is shown here simply to illustrate the least expensive type of
gage for concentricity gaging. It is built along the lines of the
standard plug gage, with the exception that it is provided with a
limit bar which controls the amount of eccentricity of the hole
and the exterior surface. Bar A is provided with a step giving
^e "go" and "not go" limits. It is also formed to a knife-

144

GAGING AND INSrECTION

edge to reduce the amount of bearing surface to a i
The plug B fits into the hole in the work and the knife-edge on
bar A is located at a distance from the axis of the plug equal to
the radius on the work.

Another simple gage that is used to test the relation of one
hole to another, the two holes being eccentric to each other, is

^ ^

.«.=

■|

o
S

—

1 t t

M-M„^^

Pig. 33. Simple Tjrpe of Concentricit; Gage based an Limit Principle

shown in Fig. 34. This gage is of simple construction and is
also built along the lines of the plug gage, having two ends,
one giving the "go" and the other the "not go" size. The
gage consists of a body A in which two plugs B and C are fastened

•l(

"=T.:--

—

--1

Ifarhlnrrt

Mi-:

Anotber Coacentricit; Gage of the Plug Type

by pins, as shown. Two disks are also fastened to the faces of
plugs B and C, one disk D being made so that it enters one of
the holes in the work, which is a combination time-fuse powder
train ring. The other disk E is made to fit in the hole which is
eccentric to the one in which plug D fits. Plugs D and F are
of the same size, whereas plugs E and G are of different sizes, the
difference in diameter being such as to control the manufacturing
limits on the work. The center location of the two disks in

INDICATING GAGES

145

relation to each other is the same on both ends of the gage, the
difference in diameter being the (actor that controls the limit
on the work. In using this gage, the work is tried first on the
" go" and then on the "not go" end. If plug £gocs in and plug
G does not, the work is satisfactory.

Testing Piston-pin Holes with Relation to Body of Piston. —
Two interesting gages, one for testing the squareness of the
piston-pin hole with relation to the exterior surface of the pis-
ton, and the other for testing the concentricity of the piston-
pin hole with relation to the exterior surface of the piston, are
shown in Fig. 35. The gage shown at .4 is for testing the square-

ness of the piston-pin hole with relation to the body of the piston,
and consists of a plug a, which is made a good fit in the piston-
pin hole, and a bracket 6, held in plug a by a screw c. Bracket
b carries a micrometer spindle d which is used for testing the
squareness of the hole.

In applying this gage, the plug is pushed into the piston-pin
hole until the shoulder e is in contact with the surface of the
piston. The micrometer spindle is then brought to bear first
at one end — near the head — and then near the base of the
piston, and the amount of variation between the two points is
read off on the thimble of the micrometer. The plug is made

146

GAGING AND INSPECTION

to enter freely enough into the piston-pin hole, so that the gage
can be turned around to bring the micrometer spindle into the
desired position.

The gage shown at B is of somewhat similar construction,
except that a dial indicator is used in place of the micrometer
screw. The dial indicator/ is held in a bracket g, as illustrated,
and is adjusted in this bracket so that its indicating point or
plunger comes directly in line with the vertical axis of the pis-
ton when shoulder h of the plug is in contact with the surface

is- 36, Teiting Coacentricily of Getri on Gear-hobbmE Machine

of the piston. After one side of the piston has been tested, the
gage is removed, the work turned around, and the other side
tested to see if the piston-pin hole is exactly central with the
exterior surface of the piston. The gage is provided with two
feet, as shown, for supporting it.

Testing Concentricity of Gear Blaaks. — One method of
testing work to see whether it is concentric or not before machin-
ing is shown in Fig. 36. This illustration shows a dial indicator
testing gear blanks which are to be cut on a gear-hobbing machiae.

INDICATING GAGES

147

After a series of blanks is fastened on ihe work-holder and the
work-holder supports are put in place, the dial indicator b
brought in contact with the work and held by clamps ;is shown.
The work-spindle is then rotated, and the movement of the dial
indicator shows whether or not the exterior surface runs true;
if not, it is an indication that the xvork has not been accurately
machined or that the work-arbor has been thrown out of cor-
rect alignment.

Testing Concentricity and Radial Positioa of Cutter Teeth. —
A testing device used by the Union Twist Drill Co. for deter-
mining whether or not the teeth of milling cutters are equi-
distant from the center, so that they will do their correct share

n. Future for Testing Coi
ol MilliDK Cutters and Positioi
Kadial Tjrpe

the work, is shown in Fig. 37. This fLXture also iletermines,
ly means of a separate indicating needle, whether or not the
teeth are radial. It consists of a base carrying an adjustable
stud on which the cutter to be tested is held, bushings being
supplied for fitting different sizes of holes in the cutters. The
cutter is then brought up to the micrometer spindle and rotated
to determine if all of the teeth are of the same height. The
work is then shifted over to the indicating pointer, and this
is brought in contact with the face of the teeth. If the teeth
are radial with the center, the indicating mark on the opposite
end of the pointer registers zero on the arm of the fixture.
A hxture which can be applied to miliing cutters or hobs having

148

GAGING AND INSPECTION

under-cut teeth is shown in Fig, 38, This gage indicates if the
cutter is true; that is, if the teeth are equidistant from the
center, and if the proper amount of under-tut is provided.
The faces of the teeth are tested by means of a linger mounted
on a slide. Readings can be taken from the scale at the left-
hand end of the gage, which is graduated in fiftieths of an inch.
The proper readings can be obtained by multiplying the radius
of the cutter by the following constant for different angles of
face, or under-cut:

Angle of Furor
Undepcul, Dekthb

Comtant, Inchu

Angle n( Face or
Under-cul. Detntt

CofUtont. lochs

0,087
0.174

o,»59

0.341
0.433

Fig. 39 shows how this reading is obtained and also how the
gage is used. For testing, if the faces of the teeth are radial,
the slide on the fixture in Fig. 38 is brought to zero, and con-

sequently does not have any lateral movement. When the
teeth are under-cut, however, the fixture is moved over the
amount given by multiplying the constant by the radius of the
cutter, and the pointer should then indicate zero if the cutter
is correct. The opposite end of the fixture carries a micrometer
test instrument for determining whether or not the points of

INDICATING GAGES

149

the teeth are equidistant from the center; in other words, if

the hole and points of the teeth are concentric with each other.

Concentricity Gage for High-explosive Shells. — Fig. 40 shows

a simple type of indicating concentricity gage for inspecting

high-explosive shells. This consists of a base A carrying an
arbor B on which there are two bushings, both slightly tapered.

icitf Gage for High-

One bushing fits the hole near the bottom and the other at the
open end or nose. The shell is simply held on the fixture by
hand and rotated to determine whether or not the exterior
surface is concentric with the bore. The concentricity of these

S. 5 s -s s>'^

.2 -s : I s i .f s
■* ^o I * 6 ^ !

rt ^ d -S a. c""^ "

■i!iii-'l^

0. 5 a< (^

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O n W }{

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TPmiCATTNG CAGES 151

shell is inclined at an angle to the base of the fixture. This
is done to keep the base of the shell constantly in contact
with the roller C, and thus locate it properly in relation to
the contact point of the indicating levers. The two points on
the shell which are tested for concentricity are the bore of the
powder pocket and the exterior surface of the shell close to
the base.

The indicating mechanism which determines the concen-
tricity of the powder pocket consists of a rod D to which a
handle E is attached, provided with a flattened end fitting
in the corresponding slot in the boss on the fixture. The in-
dicating lever G is fulcrumed at the point H and swings over
the arc / provided with three points — mean, low, and high.
The indicating device for the exterior of the shell is held on a
post / and consists of an arm K held between two adjusting
nuts L. The indicating lever M is fulcrumed at the point N
and swings over the scale 0, having marks, mean, low, and high.
In order to locate the point of the fulcrum lever M directly
in line with the vertical axis of the shell at its highest point,
the bushing P is provided, carrying a pin which comes in
. contact with stop-pins in the rod J.

Inspecting Cams on Gas Engine Camshaft. — A class of
gaging which requires accurate and careful inspection methods
is the testing of cams on gas engine camshafts. These cams
must be tested for shape, lift, and angularity of position. The
requirements are that the profile of the cam between the open-
ing and closing pouits must fit a contour gage having limits
of ±0.003 inch. When the concentric part of the cam is within
the limit of tolerance, which is o.ooi inch, the body plus the
lift must be correct to within 0.003 ""ch. The arc of the open-
ing and closing points on the cam must be correct to within
±1^ degree. The relative positions of the opening and cio^ng
points on all cams must be correct to within ±1 degree, and
this error must not be cumulative. The usual clearance pro-
vided between the top of the valve-lifter and the lower surface
of the valve-stem is from 0,003 to o.oio inch.

A simple method of gaging this work is shown in Fig. 42.

1 GAGING AND INSPECTION

This fixture is used for testing the position of the cams on an
integral four-cylinder engine camshaft. The ibcture comprises
a bed-plate A on which three brackets B, C, and D are held.
Brackets B and C are used as supports only, and are provided
with hinged caps held by thumb-screws to facilitate the in-
sertion and removal of the camshaft. The bracket D carries
a special chuck for gripping the work and is furnished with an
index plate E wluch has eight notches to correspond with the
number and position of the cams on the shaft. This disk is
located in the \';irioos positions by a tapered plunger that is

held in contact with the disk by a spring and is removed by the
handle F to index the disk. The highest point of the cam is
tested by the T-gage G, which has "go" and "not go" ends
on the bar G\. The angularity and shape of the cams are
tested by the V-gage //, which is provided with knife-edge
points and is used in connection with the indexing disk. This
gage also has "go" and "not go" V-grooves, which are made
to the exact shape desired. The brackets on this gaging fix-
ture are all located from a central groove in the bed which
keeps them in correct alignment.

Another method which employs a dial test indicator is shown

INDICATING GAGES

IS3

in Fig. 43. This device is of comparatively simple construc-
tion and consists of a base A sufficiently heavy to stand firmly,
and a vertical support B held in the base by means of screws.
The upper end of the support is drilled and reamed to receive
the shank of the dial indicator /, and is split and provided with
a screw to clamp it. The indicator point P is made in the fomi
of a spherical segment the radius r of which is one-half the
diameter of the cam roller. The center line of the indicator
must be in the same position in relation to the camshaft that
the roller is in the gasoline engine, which in this case is on the

center line of the camshaft. The distance d is then one-half
D and the height H is such as to give a good contact between
point P and cam C and allow the full limit of the indicator
movement.

When in use, the camshaft is provided with a dog and mounted
between the index centers of a suitable fixture. The first step
then is to find the center of the keyway for the camshaft gear,
as the cams are generally laid out with reference to a keyway.
Assuming that the cam is of the shape shown in the illustra-
tion, and that the center coincides with the center line of the
keyway, and also that the opening and closing points are in
the position occupied by the cam rollers R represented by the

INDICATING GAGES 155

dotted circles to the right of the illustration, the actual open-
ing iind closing points are then one-half 102 degrees, or 51
degrees in advance and 51 degrees back of the starting point.
Now, with the indicator set on the dwell of the cam allowing
for a rise of 0.003 inch — " the clearance under the valve-stem "
below zero — and with the indicator in the position shown, the
camshaft is indexed to the correct angle. If the work has
been accurately done, the indicator needle should Just begin
to rise at the 51 -degree angle; if not, it will rise either too
soon or too late, and the amount of error is read off on the
index circle of the indicator. The relation of all the other
cams to the keyway is tested in a similar manner, taking all
the opening points in their regular order, and then all the
closing points. The amount of error sometimes found in spite
of very careful work is surprising, and this method of testing
insures a high degree of accuracy.

Multiple Indicating Camshaft Gage. — A multiple indicating
camshaft gage for testing the exhaust and inlet cams for twin
four- or eight-cylinder engines is shown in Fig. 44. This con-
sists of a fixture for holding the camshaft and indexing it while
being tested, and brackets for carrying four dial indicators,
so that four cams can be tested at the same setting of the
camshaft. For the other four sets of cams, the camshaft is
shifted and the testing operation repeated. The fixture consists
principally of a base A , to which four V-blocks B are attached.
The bearings on the camshaft rest in these V-blocks. After
the camshaft is held in the V-block and located in the correct
position, a double index plate C and D is fastened to the end
of the shaft in order to give the correct angular position of
the camshaft when tesring the location of the opening and
closing points on the cams. Four cams, as previously men-
tioned, are tested at a time. The index plate is moved into
the position desired and the reading is transmitted from the
cams by the rollers E to the needle of the indicators F.

The reading on the dial indicator is taken when the cam
has raised the roller 0.005 ^^ch, thus allowing for the clearance
between the end of the push-rod and the valve-stem. As soon

GAGING AND INSPECTION

as readings have been taken from four cams and they are
fomid correct, the lever G is operated, which releases the single
clamp that holds the camshaft in position in the fixture, bear-
ing down with sufficient pressure to jircvent it from shifting,
but at the same time allowing it to be rotated by means of
the index plate. The camshaft is then shifted along the fix-
ture to bring the remaining four cams into position under the
indicators, and a similar procedure followed. The fixture is
so constructed that the index plate moves with the camshaft

when it is shifted over to bring the second set of cams into the
testing position. By means of this gage, the testing of cam-
shafts is greatly simplified in that four readings can be taken
at one setting.

Electrical Camshaft Gage. — An electric device for testing
individual cams is shown in Fig. 45. This gage consists prin-
cipally of a pivoted arm A that is raised or lowered by the
thrust of the cam being tested and is held in contact with the
cam by a helical spring. The cam is carried on the shaft B,
which is provided with a key C, the cam being slowly rotated

INDICATING GAGES

157

by means of a small motor located behind the slate base to
which the entire mechanism is attached. Connection is made
with an electric battery in such a manner that, when the cam
raises and lowers the arm A, it closes the electric circuit by
making contact with the aiijustin^' si ri'w- /). K, F. and G,
respectively. If the throw
of the cam is too slight, no
contact will be made with
cither of the adjustini,'
screws D and £; if the
throw is as it should be,
contact will be made with
the screw D, and the green
lamp on the top of the
board will flash. If the
throw is too great, contact
will be made with both
screws D and E, resulting
in the flashing of both the
red and the green lamps.
In the same manner, the
lamps at the bottom of
the board are flashed; if
the diameter of the cam
is too great, neither light
flashes; if correct, the green
light shows; and, if too
small, both the green and
red lights show. The con-
tact screws are made from brass carrying a copjier contact point
which is pressed out by means of a brass spring. This device
is adjusted by means of a master cam which has been measured
by hand and found to be correct.

Device for Testing Electric Starter IgnitioQ Cams. — Fig. 46
shows an application of the indicating dial type of gage in con-
Junction with a multiplying lever for testing ignition cams for
"Delco" electric starters. The indicator used gives readings

Fig- 46. Special Type of iDdlutUtg Gage
loi Inapecling Inteirupter Cams for Elec-

15»

AGING AND INSPECnfflfl

to o.ooot inch. The gage is rigidly built aad consists of a base
A into which a stand B is screwed that carries the measuring
table C provided with a split box at the rear through which
passes the post supporting the multiplying lever arrangement.
The dial test indicator D is fastened to the rear bracket and
is operated by a multiplying lever E. This is fulcrumed on
adjustable pointer screws F and is provided with a boss at
its lower surface in which a plunger G iits. This plunger is
adjusted by a screw H which, in turn, is clamped by a screw
/. In this case, the cam to be gaged is held on a stud J and
is brought into contact with a locating point K. Previous to
testing the work, the gage is set at zero by means of a master.
The limits on this work are ±0.0005 inch.

Ordinate System of Gaging. — As explained in Chapter IV,
irregular-shaped parts are generally gaged by means of pro&le
templets, the work being inspected by holding it in contact
with the templet and up to the light. A very small variation
in the work from the gage can be detected by the rays of light
between the two pieces, but there is no definite means of
determining just what this variation is. Consequently, the
templet system is not satisfactory for interchangeable manu-
facture, as the discrepancies in the work are not measurable.
The type of profile gage used is governed largely by the stiape
and character of the work. In gaging approximately cylin-
drical work, a profiJe gage called a "receiver gage" is generally
employed. In this case, the gage is bored, reamed, and lapped
to the shape of the work and Is then slabbed off so that the hole
in the gage is exposed; then when the work is inserted, its
outline can be compared with that of the gage. The most
common form of templet is made from sheet steel and is filed
and ground on the measuring side to a knife-edge similar to
that used on a straightedge. When the work to be measured
has several shoulders or irregularities of outline, it is neces-
sary that the gage be held parallel with the axis of the work.
There are other objections to the templet system, and in up-
to-date manufacturing plants templets are used as sparingly

INDICATING GAGES

159

By the ordinate system of gaging, a piece of irregular out-
line is gaged at all the principal points for the desired meas-
urements by means of either one of two systems. One system
employs the flush-pin principle and the other the dial test
indicator. The system used depends upon the number of
surfaces to be gaged and the convenience with which these
surfaces can be approached. Fig. 47 shows a simple method
of gaging a piece of irregular outline. In this case, the flush-
pin principle can be adopted because of the comparatively

simple outline of the piece. These flush-pins are held in sepa-
rate blocks fastened to a base, and the axis of the flush-pin is
located at right angles to the surface to be gaged.

The rear end of the bracket carrying the flush-pin is pro-
vided with a plus and minus limit step. The flush-pins are
pushed back to insert the work in the holder, and are then
pushed forward to ascertain whether or not the work has been
machined properly. The test consists ui comparing, by the
sense of touch, the positions of the ends of the flush-pins with
relation to the steps on the rear ends of the holders. A simple

GAGING AND INSPECTION

ejecting mechanism is used in connection with this gage; it
consists of a rod A passing through the body of the plate and
carrying two eccentrics. These work against pins held in the
base that are forced upward by the eccentrics to eject the work
from the dowel-pins on which it is held. Two pins in the end
of the gage block act :is stopping points for this rod.

Another type of gage working on the ordinate principle is
shown in Fig. 48. In this case, the dial test indicator principle
is employed, because the points that must be measured are
not accessible with the flush-pin type. The construction of

tiiis gage is comparatively simple; it corLsists chiefly of a base
A carrying a hardened and lapped master block B which is
of the same shape as the work and is hardened, ground and
lapped to the mean dimensions of the work. This block is
provided with close-fitting dowel-pins which are made to fit
the locating holes in the work to be gaged. In the lower left-
hand comer of the gage is a block C, which is used for setting
the block D and spindle E of the dial test indicator in line
with each other. The surface of this block is hardened, ground
and lapped, and is at right angles to the surface of the plate.
Lines are drawn from the points where the gaging is to be done.

INDICATING GAGES

l6i

and opposite these lines are numbers. These numbers indicate
the limits in thousandths of an inch provided on the work.
For instance, (3 — ) means that at this point the piece can be
0.003 ""^ '•^ss or smaller than the master by which it is being
compared.

In using this gage, the block carrying the dial test indi-
cator is swung around and the dial test indicator spindle and

Fig. 49.

measuring end of the block arc brought in contact with the
setting block C The bezel of the diaJ test indicator is then
rotated so that the needle pwints to zero. The gage is then
swung around and brought in contact with the work. Index
points are marked on the rear and front ends of the block D
so that these are brought in line with lines on the plate A.

Il62

GAGING AND INSPECTION

I Then the block D is brought in contact with the master, and
I the spindle of the dial test indicator in contact with the work,
the resulting readings being
taken off on the indicator.
The indicator and block which
arc fastened to each other
can be moved around to any
point on the work and the
variations between the work
and the master can be read
oft in thousandths of an inch.
The advantage of this system
over the templet system is
evident, in that it gives a di-
rect reading and indicates to
the inspector just how many
thousandths of an inch the
work varies from the required
size.

Dial Indicators for Testing
Pressure. — The dial indica-
tor is used to a large extent
for testing pressure in the
inspection , of springs that
must be capable of exerting
a required pressure when com-
pressed a certain amount.
The application of the dial
indicator to this work is
shown in Fig. 49. This illus-
tration shows a special fixture
used in testing the pressure
exerted by conical valve
springs for gas engines. The
fixture consists principally of
a regular scale dial, which is attached to a base A having an
upright B. This upright carries a spindle which is operated

Pig 50 Indicating Gige for Teiting
Campressire Sttengtb of Spnngs
Died m CombinaboD Time and
PercuisloD Fuses

INDICATING CAGES

by a rack and pinion through the turnstile C, the distance
that the spring is compressed being determined by the stop
D, which comes in contact with a pin on the top of the fix-
ture. The spring being tested is compressed about ij inch
— the compression it has in the gas engine — and must show
a pressure of 58 pounds on the dial.

Device for Testing Time Fuse Percussion Restraining
Springs. — A much more delicate instrument than that illus-
trated in Fig. 49 is shown in Fig. 50. In this case, the device
is used for testing the pressure of percussion restraining springs
used in combination time and percussion fuses. It consists of
a base A carrying an upright B; the base A rests on four feet
C, which are capable of being adjusted so that the instrument
can be set "parallel," this being determined by means of the
cross-level D. Post B carries two plates E, which support
the spindle carrying the washers F and G. These plates are
countersunk so that only a knife-edge bearing is provided for
contact with the plunger. The total weight of washers F and
plunger H is 1.5 ounce; the "limit weight" C is 0.15 ounce.
The spring to be tested is placed on test pin /, the spindle H
meanwhile being held up by hand. The spindle is then allowed
to compress the spring, and if it is correct, the points marked
must coincide when the distance A' is 0.370 inch. If the weight
of F and the spindle is not sufficient to give this reading, the
limit weight G is added; if this makes the distance A' correct,
then the spring is satisfactory; if not, it is too stiff. If the
distance A' is less than 0.370 inch when weight G is not on the
spindle, then the spring is too weak.

Indicating Gage depending upon the Sense of Hearing. —
As has been previously mentioned, indicating gages depend
upon the sense of touch, sight, and hearing for their operation.
Those depending upon the sense of hearing are generally of
the electrical type, and an example of a gage employing this
principle is shown in Fig. 51. This gage is employed for test-
ing the closing pressure of piston rings. Piston rings have
been tested for closing pressure by many other devices, all
of which have been more or less satisfactory. It is generally

mcrCATING GAGES

known that a piston ring which does not possess the required
- amount of tension does not He in dose touch with the walls
of the cylinder all around, and hence gas is allowed to leak
past and compression is lost. It b, therefore, desirable to know
if the rings have sufficient tension before they are inserted in
the piston, and the gage in Fig, 51 determmes this satisfac-
torily.

The gage has a cast-iron plate A machined on its top surface
to provide two ribs B that are nicely finished so that the rings
can be slipped along them without undue friction. Fastened
to one side of the fixture is a bracket C, which is machined out
on one edge, providing a step that is of a slightly greater height
than the width of the piston ring to be tested. Held on the
other side of the cast-iron plate is a lever Z>, which is fulcrumed
at the point E by two cone-pointed screws in the bracket F.
At one end of the fixture, pulley G is attached, and run-
ning over this is a wire rope which carries the weight H; the
size of the weight depends upon the size of piston ring being
tested. This wire rope is attached to the rear end of lever D,
which carries a contact point /. This contact point makes
contact with the point J of the "Champion" spark plug K
when the piston ring is of the desired tension. Plug A' is con-
nectcti by suitable wiring to a bell and battery in the box under
plate A.

When using the gage, the inspector lays the ring flat on the
testing surface of the plate and pulls it toward him between
the fixed and movable strips C and D, respectively, with the
split or saw cut exactly in the center. In pulling the ring
through the fixture, if the pressure is sufficient to overcome
the resistance of weight H, which on the Ford piston ring
is 18 pounds, electrical contact is made between points / and J,
and the bell in the box of the fixture is rung. If the inspector
pulls the ring through the fixture without the bell ringing,
then the ring does not come up to the required tension, and
is consequently rejected. When this fLxture was adopted in
one plant, it was found that previous methods had been in-
accurate, and anywhere from so to 50 per cent of the rings

i66

GAGING AND INSPECTION

formerly made proved to be failures. Changes in manufac-
turing methods, however, reduced the numljer of failures from
S to 10 per cent.

Gaging and Inspecting Balls and Ball Bearings. — Aside
from the manufacture of rifles and similar interchangeable
work, there is probably no industry in which gaging and in-
^)ection methods are developed to a higher degree of perfec-
tion than in the manu-
facture of balls and
ball bearings. As a
rule, this industry is
divided; that is, one
manufacturer makes
the balls and another
the bearings. There
are some manufac-
turers who make the
entire product, but this
is the exception rather
than the rule. No
other industry makes
more extensive use of
indicating gages than
the ball and ball bear-
ing industry, and, in
the following, atten-
tion will be given to
the types of gages used ,
for this work.
Gaging and Inspecting Balls. — In the gaging and inspection
of balls, there are two main points that must be considered:
First, the ball must be spherical within certain limits, and,
second, it must be made to a definite diameter, also within
limits. The manufacturing limits to which the balls are made
depend entirely upon the use to which the balls are put. For
high-grade balls they must be held to within a limit of 0.00005
inch of being perfect spheres, and must not vary more than

nmiCATINO CAGES 167

0.00005 '"'^h ^ diameter. For bicycles, hardware, and similar
work, the manufacturing limits can be considerably wider.
In the following, however, attention will be directed particu-
larly to the gages used in making high-grade balb.

During the process of manufacture, the balls are gaged to
see that the grinding or lapping machines are working properly.
Figs. 53 and 53 show a special gage develo|>ed by the Hoover
Steel Ball Co., of Ann
Arbor, Mich., for this
work. Referring to
Fig. 53, which shows
the construction of
the gage more clearly,
it will be noticed that
it is of the adjustable
type and is pruvidnl
with two anvils, mn
of which is adju^tnl
by means of a screw
held in place by clanii>-
ing nuts. The gage
consists principally of
plate A mounted on
three feet, the rear
one of which is shorter
than the other two, so
that the gage is in-
clined at a slight angle.
The ball to be gaged
is shown held in the nest B, and the gage is so inclined that
the ball always rests in the rear of this nest.

The upper and lower anvils are provided with diamond
gaging points held in brass holders. These diamonds are so
mounted that a flat face is presented to the ball surface to be
gaged. The multiplying lever principle is used here in the
ratio of 150 to i, so that, for variations of 0,0001 inch in the
ball, the top point of needle £ would move over the arc a dis-

Flg. Si- Indkiting Gkga thotrn io Fig. 5)
wilh Plai« removad to show Conitruc-
tiomJ FeitiuBB

ifa

i68

GAGING AND mSPECTTON

tance of 0.015 inch. The construction of this indicating lever
mechanism is as follows: Lever D is connected to anvil C and
meshes with lever E through a rack tooth. There are no
springs in this gage, and the upper anvil is kept in contact
with the work by means of a weight F attached to the indi-
cating needle £, By means of this gage, it is possible to de-
termine rapidly if the balls are being ground out of round or

under diameter when in the rough state. While the wear on
the diamonds is very slight, it is nevertheless necessary to be
certain that the instrument is measuring correctly, and at
certain intervals the indicating needle is set by means of a master
ball. The adjusting screw holding the lower anvil is then
adjusted the required amount.

INDICATING GAGES 169

Indicating Gage for Inspecting Finished Balls. — After the
balls come from the grinding and kpping departments, the
first inspection consists in looking them over to see that they
are free from pits, scale, bands, dents, tool marks, etc. This
is done on the smaller sizes of balls (up to | inch in diameter)
by rolling the balls on a glass plate. A ball that is not perfectly
spherical will not roll straight, but will wobble from side to side.
Balls over | inch in diameter are inspected by means of the
indicating gage shown in Fig. 54, This device consbts of a
dial gage combined with a multiplying lever mounted on a
plate held on a stand which is set at an angle so that the ball

being gaged always lies at the back surface of the pocket in
which it is retained. The lower and upper anvils carry black
diamonds, the flat surfaces of which bear upon the ball. The
multiplying lever is in the ratio of 10 to i, and as the indicator
normally reads to 0.001 inch, this multiplication makes it pos--
sible to obtain readings to o.oooi inch. The limit on the ball
is 0.00005 inch both for roundness and diameter, so that the
maxunum movement of the needle for satbfactory balls would
be not more than one-half the amount between any two marks
on the dial.
In multiplying lever gages made on this principle, it will

170

GAGING AND INSPECTION

be seen, by referring to Fig. 55, that very wide variations in
diameter cannot be accurately indicated. The reason for this
is that the length of the arm uf the multiplying lever changes
as the measuring point is moved up or down. Consequently,

it is essential that a master ball be used for setting this gage

for each size of ball to be gaged, and then that the gage be used
only as a means of comparison and not as a direct measuring
instrument. Girls operating these instruments can gage 10,000
balls in ten hours, or 1000 balls an hour, and determine whether
the ball is out of round, within the limits for diameter, or if

INDICATING GAGES 171

it has any other imperfections which have passed the notice

of the previous inspectors.

Hirth Millimeter for Gaging Balls. — Fig. 56 shows a Hirth
minimeter (or inspecting balls for accuracy of diameter and
spherical form. It consists of a special stand carrying a lower
anvil which is adjustable as shown, a support for the ball to
locate it so that its axis comes in line with the upper and lower

vils, and an arm in which the minimeter proper is retained.

le top measuring an\il of the minimeter is lifted by means of
the finger, as shown, and when the ball is inserted all external
pressure is removed. This instrument is constructed so that
readings as fine as 0.00005 in'^h are obtainable.

Automatic Ball Gaging Machines. — High-grade balls under f
inch in diameter arc gaged for accuracy of diameter by automatic
ball gaging machines, two tjpes of which are shown in Figs. 57
and 58, The machine shown in Fig. 57 is used for gaging
balls up to 5 inch in diameter and comprises a hopper for hold-
ing the balls, and a slide through which they roll when being
gaged. The measuring portions of this slide consist of two
straightedges, the space between the edges of which gradually
increases in width as the slide extends from the hopper. Pass-
ing beneath the hopper is a slide which is agitated by a rack
and segment gear, operated by an eccentric motion. The
balls to be gaged are dumped into hopper A and carried forward
to the delivery spout by means of a slide B. Slide B carries
one ball forward at a time, drops it through spout C and into
slide D. Here the distance between the two slides is about
0.005 "I'^h smaller than the smallest diameter of the balb to
be gaged. The balls then roll along between slides D until
they come to the straightedges E. These straightedges are
set so that they form a slightly tapered slot or opening. The
angle or taper to which these straightedges is set is determined
entirely by the limits required on the balls. If the balls must
be held within very close limits, then the amount of variation
in the taper of the straightedges is slight. Sometimes they
are set so that a difference of 0.005 ^^ in diameter will be
measured from one end to the other. As the balls roll down

1 172

GAGING AND INSPECTION

these slides due to the action of gravity, the angle to which
they are set being about 20 degrees from the plane of the table,
they drop through the slide at the point where the distance
between the two straightedges is slightly greater than the diam-

Flg. 57. Aulomi

eter of the ball. As they drop through, they are separated
by tubes which enter the various drawers in the cabinet located
beneath the table top. When these drawers are full, they are
removed and the baliri liiken nut and pul in proper boxes,
accordhig to the grading determined by the machine.

INDICATING GAGES

173

Another type of automatic ball gaging machine is shown in
Fig. 58. This device is used for gaging balls up to | inch in
diameter. In this case, the slides are set almost parallel with
the table, and the balls are carried between the straightedges

1 X

W^M

■

►y means of an agitator which comes up and lifts them from
'the surface of the straightedges. The top surface of the agi-
tator is at an angle of about 5 degrees, and when the agitator
rises the balls roll along it until they drop through between the

174

GAGING AND INSPECTION

Table L S. A. B. Standard Sizes and Tolerances for Ball Bearings

(Light Series)

i. i

yy^y/Z

..._L

MatAinery

Ball
Bearing
Number

Bore of Inner Race Ring

200
20 1

202
203

204
205

206
207

208
209

210
211

212
213

214

215

216
217

218

219
220

221
222

Bore A,
Inches

0.39370
0.47244

o 59055
0.66929

0.78740
0.98425

I
I

I
2

2
2

.181 10

■37795

•57481
.77166

.96851
.16536

.36221
■55906

2.75591
2.95277

3.14962
3 34647

3 54332
3.74017

3 93702

4.13387
4.33072

Tolerance, Inch

Plus

0.0002
0.0002

0.0002

0.0002
0.0002

0.0002
0.0002
0.0602

Minus

O.OOC4
0.0004

0.0004
0.0004

0.0004
0.0006

0.0006
0.0006

0.0006
0.0007

0.0007
0.0007

0.0007
0.0007
0.0007

Diameter oC Outer Race Ring

Diameter B,
Inches

I .18110
I . 25984

1.37795
I. 57481

I .85040
2.04725

2.44095
2.83465

3 14962
3 34647

3 54332
3.93702

4.33072
4.72443

4.92128
5.11813

5-51183
5.90554

6.29924
6.69294

7 . 08664
7 48035
7.87405

td.

Plus

o
o

o
o
o

, Inch

Minus

0.0006
0.0006

0.0006
0.0008

0.0008
0.0008

0.0008
0.0012

0.0012
0.0012

0.0012
0.0012
0.0012

INDICATING GAGES

175

Table n. S. A. S. Stindard Sizes and Tolerances for Ball Beitfings

(Licht Series)

V<I^/.

^\\\\\K^

.1 i

._--i.

JfaoiliiMry

BaU
Bearing
Number

200
201

202
203

204
205

206
207

208
209

210
211

212
213

214
215

216
217

218
219

220
221
222

Width of Both Race Rings

Width C. Inch

o 35433
0.39370

0.43307
0.47244

0.55118
0.590SS

0.62992
0.66929

o . 70866
0.74803

o . 78740
0.82677

0.86614

0.90551

0.94488
0.98425

I .02362
I . 10236

I.I8II0

I . 25984

1.33858

I. 41732
I .49607

Tolerance. Inch

Plus

o
o

o
o
o

Minus

0.0020
0.0020

0.0020
0.0020
0.0020

Comers D* on

Outer Race

and Bore of

Inner Race,

Inch

0.040
0.040

0.640
0.040

o
o

.080
.080

0.080
0.080

0.120
0.120

0.120
0.120
0.120

Eccentricity Tolerance,
Inch

Inner Race
Ring

0.0008
0.0008

0.0008

O.OOIO

o.ooio

O.OOIO

0.0010
0.0010

0.0012
0.0012

0.0012
0.0012
0.0012

Outer Race
Ring

0.0012
0.0012

0.0012
0.0016

0.0016
0.0016

0.0018
0.0018

0.0018
0.0018
0.0018

* A chamfer of 45 degrees ground true with the bore and outside diameter is recommended.

176

GAGING AND INSPECTION

OS
H

c
o

3-§
^5

J3
u
C

Iff

o
o

3
C

■y:

.fl -
on

< t

•-S •'* ^

MM C«C4 C«^ \0 \0 <C<0 ^<0 0000 000000

MM MM MM MM MM MM MM MMM

88 8 8 8 8 8 8 8 8 88 88 888

do do do od 6 6 6 6 6 6 6 6 6

o oo oo oo «« «««

M MM MM MM MM MMM

8 88 88 8 8 88 888

6 6 6 6 6 6 6 6 6 6 6 6 do o o o

00 QQ QQ 00 oo OO OO OO

?? ^^ ^^ ^? ^2 22 2 2 2 2

OO 00 OO OO OO OO OO OOO

Q O

o o

II II II I2

o o

000

« « «

•

r«

p«

c«

f«»

•

00 00 00 00 00 00 00 000

o o
o o

o o

CI c«

o o

000

M C« «

000

00 00 00 00 00 00 00 000

x: 8

iJ-c

•O

;?:

w c«

c« ct

M C«

^l» >^ NIP
|K .^ .^

C« CO «0

00 X OC 00

00 00

o o

00 00 00 00 00

d d

C« M

CI CI M

88 888

000

00 00 00 00 00 00 00 000

»oto »oci ciM nro cOPO ^^ ^^ xn ^ Q

ciO^iOvO POO '^'f "^00 n'<^ ^^ »o O VO

t>.o ^o^ f>ot>. o^oom »oa^ civo O^^

rf'f co^ ^«0 roci mm QO^ ^00 00 I>»VO

O't qom »oa^ cor^ Mio a»c« voO ^oo ^

cici cico coco ^^ \r) \n to^O ^O ^* t^ I>»00

vCO OvC lOvO »>•»>* i>»t>. t>.r>»f>»

8^ 88 88 88 88 888

do OO 00 00 OO OO 00 OOO

nCI C|C| CI»S CICI "NCI CICI CICI CICIM

OO OO 00 00 00 00 OOO

O»o O \n *- ko mvO m^O Mi>. cii>. cir>»«

rfci MOtOOtO »Oco «^0 O^t^lO^ »OmO

r>.^ Mt^ rfM 00»o cid* loci o^^O ro O l>-

0000 oot^ t>.r>.tO^ to»o iTi \n ^ ^ "t^co

t>»o% MCO »Ot>» O^M co»0 I>»0^ MPO i/>I>»0*

6 6 MM MM MM MM MM coco «*>tO«*>

rftOlO»^00a^ 0«-» MCO ^»OVO»^000*0

OO OO oo MM MM MM MM MMM

CO^O COCO co^O coco fOfO coco coco cocO«*>

II II JLtaH MM MM MM ^^^

INDICATING GAGES 1^7

straightedges at the point corresponding to their size. This
particular machine is provided with eight compartments, and
the variation between each compartment is o.oooi inch. For
gaging, the balls are placed in the hopper .4, inside of which
k an agitator operated by the belt B. This distributes the
balls so that they come out of the spout C one at a time and
drop into slide D. From this they are carried on by the agi-
tator onto the straightedges E until they drop down into the
required compartment.

Gaging and Inspecting Ball Bearing Race Rings. — The
gaging of ball bearing races requires measurements of great
refinement. The lim-
its on the race rings
are very close; for
instance, on the hole
in the inner race,
which fits on the
shaft, the hmits are
+0.0002, ajid— 0.0004
inch. For the out-
side diameter of the
outer race ring, the
limits are +0.0004,
and —0.0008 inch.

In the ball bearing raceways, the variation is as great as
0.0003 inch. The limits on the hole of ball thrust bearing
races are +0.0002 and —0.0004 inch. For the outside diam-
eter, the limits are +0.0006 inch and —0.0012 inch. The
limit for the height of single thrust bearings is +0.002

1 inch, and for the height of double-acting thrust bearings,

I +0.004 iiich- Tables I, II, and III give tolerances for ball
and roller bearings, respectively, as established by the Society

, .of Automotive Engineers (S.A.E.). In the case of ball bearings,
only the light series is listed; and in the case of roller bearings,
only the narrow series is given. The tolerances, however, on

I the medium and heavy ball Ijearings and medium and wide

b roller bearings are the same.

t\.

"i^^

f -^

'))

1 \

■■'

t-^»

GAGING AND INSPECTION

For gaging ball bearings when machining, the micrometer
caliper is extensively used for measuring all outside dimen-
sions, and for internal measurements, plug gages or three-
point indicating gages are generally adopted. The plug gage
has been found unsatisfactory for gaging ball bearing race
rings. The reason for this is that the operator does not know
how much material remains to be removed, and, consequently,
is working without any guidance until he reaches the "go"
dimension on the gage. The result is that all grinding ma-
chine operators prefer to use some sort of indicatirig gage which
gives them some latitude. One ball bearing manufacturer has

devised a three-point indicating gage for use on the grinding
machine for internal work which is used entirely by the machine
operators and has been found to give satisfactory results.

For external grinding, snap gages are seldom used. Attempts
have been made by one manufacturer to replace the micrometer
caliper with a dial test indicating gage. This proved unsatis-
factory, however, owing to the excessive fluctuations to which
the needle is subjected when it is necessary to slide the gaging
point over the work. On a dial test indicator which is made
to read to 0.0001 inch, very little irregularity in the surface
of the work causes a considerable movement of the needle,
and as there is no "damping," or effective means of preventing
oscillations of the needle, it is difficult to use this type of gage

INDICATING GAGES

179

for snap work. Consequently, it is the rule in practically all
plants making ball bearing race rings to use micrometer calipers
in the manufacturing departments. The inspectors are fur-
nished with plug and snap gages of the limit type.

Plug gages for ball bearing races must be made light, so as
not to fatigue the inspector. With a plug gage, say 3 inches
in diameter, made from solid tool steel, the weight is objec-
tionable, and several manufacturers reduce the weight of large
plug gages by making the gaging part in the form of a ring
which is held on an aluminum core. The aluminum core is
extended to form the handle and is knurled as usual. In some
plants, plug gages that have become worn are annealed and
turned down to the next size. They are then hardened, ground
and lapped, and in this way can be used a great many times.

Gaging Raceways in Annular Ball Bearing Rings. — The
raceways or grooves in ball bearing rings must be carefully
checked. The shape of the curve is usually checked by templet
gages, as illustrated at A and B in Fig. 59. For testing the
diameter of the raceway in the inner and outer rings, various
means are employed, the most common being thai in which
three balls are used to determine the correct depth. Another
method makes use of a micrometer caliper having three ball
points.

Gaging Raceways in Thrust Bearings. — For thrust bearing
race rings, it is necessary that the raceway be concentric with
the bore of the ring; also that it be of the correct depth and
of the proper radius. A satisfactory indicating gage for test-
ing race rings is shown in Fig. 60; the race ring being tested
is that used on the main drive shaft of an automobile. The
gage rests on a cast-iron stand A in which a hardened and ground
Steel ring B is held. The top part of this ring is made a good
fit for the inside diameter of the ball bearing race ring C. A
stud D, held to the base by a nut as shown, is slotted to receive
the gage plate E. Stud D is hardened and ground and plate
£ has a reinforcing plate F held to it by rivets, the latter being
hardened and ground and made a good fit in the slot in the
stud. The fulcrum of the pointer or needle C is so placed that

i 180

GAGING AND INSPECTION

any variation in the work is magnified twenty-five times at
the point where the reading Is taken. A knurled handle H
is fastened to the gage for convenience in holding the gage.

The work is slipped over the ring B of the gage, as shown;
then the gage plate E is placed in the slot in stud D, and the
gaging knife-edge rollers /, which in this case do not rotate
but are held rigidly to the frame, are placed in the ball race
groove. The position of the indicating point of the needle
is then noted to see if the race is of the required diameter. A

limit of o.ooi inch is allowed on the diameter of the ball race
groove. The base of this gage is fastened to a frame, not shown,
which is of sutTicient height to bring the ring to be gaged in line
with the operator's vision.

Testing Diameters of Inner and Outer Race Rings. — As
has been previously mentioned, the outer diameters of the
inner and outer race rings are generally inspected by snap
gages or indicating gages. Fig. 61 shows the Hirth minimeter
being used for this work; the graduated scale on this minimeter
s such as to give readings to 0.0001 inch, and it has been found

INDICATING GAGES

very satisfactorj' for work of such refinement. For gaging
the interior or hole in the outer and inner races, plug gages are

sometimes used, but a more satisfactory gage is shown in Fig.
20. This shows a Hirth mlnimeter with a special attachment

by means of which it is possible to telt whether the diameter
is correct or not, and whether the hole is out of round, tapered,

Testing Concentricity of Ball Bearings. — In order to deter-
mine if the ball bearing will run true within the required limits,
the cone or center race is tested for wobble or concentricity.

Usually this is done by supporting the inner ring or cone on
an arbor and using an indicating gage similar to that illustrated
in Fig, 62, where a completed ball bearing is shown being tested.
In testing a ball bearing for concentricity after the bails, re-
tainers, and inner and outer races have been assembled, the
inner race is forced by hand carefully onto a hardened and
ground arbor. This arbor is then placed between centers, as
shown in Fig. 62, and the carrier A holding a Hirth minimeter

INDICATING GAGES 183

is brought up so that the needle stands at zero when it is brought
in contact with the outer race. The outer ring is then rotated
independently of the inner one, also on centers, and the amount
ol side wobble or eccentricity is noted on the minimeter scale.
The amount of wobble allowed in a ball bearing depends
upon its size; it is usually not greater than o.ooi or o.ooa inch
for large bearings, and is less than this for smaller sizes. The
axial wobble or thrust, that is, the displacement of the imier
race with respect to the outer, is not of so great importance
as the radial wobble. Experiments in various shops have

Fig. 63.

shown that a slight axial clearance does not appreciably affect
the durability of the ball bearing. In general, a clearance of
0.002 or 0.003 '"'^h may be regarded as advantageous.

Testing External Diameter of Completed Ball Bearings. — A
simple but satisfactory means of gaging the external diameter
of a completely assembled ball bearing is shown in Fig. 63.
This gage is built in the form of a snap gage and has in the
middle a movable V-support, which is set in accordance with
the diameter of the bearing being measured. One of the two
measuring points has a coarse adjustment by means of an
adjusting screw, which fits in holes 0.040 inch apart, and a

GAGING AND INSPECTION

"fine adjustment by means of a micrometer. The measurement
is taken with a Htrth minimeter, which is brought in contact
with the opposite side of the ball bearing. The bearing is
rotated while being tested, so that its roundness can be tested
at the same time as the diameter. This particular gage is set
by means of a master ring.

Box Type Inspection Fixtures. — The gaging of single holes,
shafts, and similar work is a comparatively simple proportion
as compared with the gaging of parts having a multiplicity of
holes that must bear some deftnite relation to each other and
to finished surfaces. Formerly many manufacturers depended
upon their jigs and fixtures to obtain the desired amount of
accuracy. Jigs and fixtures, however, cannot be depended
upon to remain accurate for any considerable length of time,
especially when they are roughly handled, and if the work that
comes from these fixtures must be accurate, it is highly de-
sirable that the fixtures be tested frequently. Another point
which must be considered is the fact that a box type of jig is
likely to drill and ream work inaccurately if not kept clean
by the operator. The collection of dirt in one comer of a box
jig would easily throw the work out to such an extent that
holes which are to bear a certain relation to a milled surface
would be located inaccurately. Consequently, the most de-
sirable practice is to gage the work after it comes from the jig.
The importance of this will be more fully appreciated when
it b remembered that most drilling machine work is done by
inexperienced mechanics — men who know little about accu-
rate work, and simply have sufficient knowledge to put the
work in the jig, take it out again, and operate the machine.
The Dayton Engineering Laboratories Co. has developed an
interesting system of box gaging which is used to a large extent
throughout the various manufacturing departments in its
plant. This type of gage has been developed primarily in an
endeavor to produce electric starting, ignition and lighting
equipments on a truly interchangeable basis. In the following
are described some of the gages used in this plant which in-
:orporate interesting features.

INDICATING GAGES 185

Gaging Milled Surfaces in Relation to Dowel-pin Holes. —
Fig. 64 shows an interesting box gaging fixture which is used
to determine the location of a rtamed hole and milled surface
on a generator end-frame in relation to the dowel-pin holes.
The fixture is provided with hardened and ground dowel-pins A
which fit in the dowel-pin holes of the work, and a hardened
and ground plug B operated by plug C. When the work D
is placed on the dowel-pins, plug B is raised into the hole, and
if the hole is correct, the plug will pass through; if not, the

tas — T- *r

Fi(. (n. Speciti Type 0! Box Gaging Fiilure uasd (or InipccUni
Bctation ot Bora to Milled Surfaces on in Electric Stuter Gen-

plug will not rise. The limits on the work are provided for
by having the plug the required amount smaller than the hole
in the work. The milled surface on the work is inspected by
means of the rotating plug gages F and G. These are each
provided with two bosses, one of which is made to indicate
the "go" and the other the "nut go'" dimension. These pro-
jections are then swung past the milled surface on the work,
and if the "go" end passes by and the "not go" does not,
the work is within the required limits. In this case, the toler-

INDICATING GAGES 187

' ance allowed on the milted surface is 0.002 inch, and on the hole
the limits are ±0.001 inch.

Box Inspection Gage for Generator Frame. — An interesting
and practical application of the box type of gaging fixture is
I shown in Figs. 6g and 66. This gaging fixture is used for
I inspecting the location of the various holes in the generator
frame, and is constructed along the same lines as the drilling
jig used in producing the holes. The points to be gaged are
three threaded holes which must bear a definite relation to the

^^Kniillt
^^■ft cc

iilled surface, and, in addition, the milled surface must bear
k certain relation to ' the center hole. The three holes are
gaged, respectively, by the plugs A, B, and C. The location
of the milled surface is inspected by the limit gage D, Fig.
66, which is of the feeler type and is inserted between the hard-
ened and ground plate F and the work G, Reference to Fig.
65 will show the variation allowed in the fixture in the location
of the three tapped holes, which is ±0.0005 '"'^h. The limits
on the work are still wider and are controlled by means of the
variation between the pitch diameter of the plug gage and the

i88

GAGING AND INSPECTION

threaded hole in the work. The location of the miJIed surface
on the work in relation to the central hole also has limits of
±0.0005 i^ch in the manufacture of the gage, whereas the
work has a tolerance of 0.002 inch. The bore is inspected
by swinging end-measuring bar H, Fig. 65, which is fulcrumed
on a central stud and has "go" and "not go" ends.

Fig. 67. Another Type of Generator ?r*me Inspection Fiituie

Reference to Fig, 66 will show that this gage is constructed
of cast iron, but all wearing surfaces are made of tool steel
or machine steel, casehardened and ground. It consists pri-
marily of a base on which a measuring surface is screwed and
a swinging plate fulcrumed at the rear of the hxture and held

I [WO ai

INDICATING GAGES

down by means of two hardened and ground plugs. The
swinging plate is provided with two clamping screws in the
center and two spring plungers. The clamping screws are
brought down lightly and the springs are depended upon to
keep the work tightly against the lower surface of the fixture.

Fig. 67 shows another generator frame gaging fixture which
is constructed on the same principle as that illustrated in Figs.
65 and 66. In this case, the generator is of different shape,
and the fixture is shown with the lid up, exposing its interior
construction. Reference to this illustration will show that the
pole-piece bearings are inspected by means of a swinging gage
A having "go" and "not go" ends. The bar is grasped by
the inspector and is swung around past the poles to determine
if they are of the correct diameter. The lid is then swung
down and the feeler gage B used to determine if the frame is
of the required length in relation to the central hole or axis.
On the opposite end is a hole which must be gaged; this is
done by a plug gage which is smaller than the hole in the work
by an amount equal to the limits allowed.

Two additional gaging fLxtures are shown in Fig. 68. The
one to the left is built along similar lines to the generator
frame gage shown in Fig. 65. This gage shows the work re-
moved and illustrates the method of locating and gaging it.
The work fits over the stud 0, and is provided with a slot in
which plunger A fits. A feeler gage is then inserted between
the hardened plate B and the work to inspect the position of
this slot, as well as of the milled surface in relation to the
central hole. There is a bushed hole C in the top cover plate
through which a plug is inserted for gaging a corresponding
hole in the work. The fixture is provided with gaging seats
in which dowel-pins arc located for centering the work. The
hinge plate is bushed, and is located accurately by hardened,
ground and lapped plugs.

Another inspection fixture is illustrated to the right in Fig.
68. This gage is also used for inspecting a generator frame,
and determines the relation of a second bored hole hav-ing
two diameters at right angles to the first which is located from

IQO

GAGraC AND INSPECTION

stud F. The work is located by two dowei-pins, and the
central plug is raised by operating lever C. The non-rotating
traverse plugs D and E and the central one determine the
relation of the center distances between the spiral gears in
the generator frame, and the relation of these holes may vary
more in one direction than in another. In addition, two other
rotating "go" and "not go" plugs // and / are used to deter-

mine the location of the milled surface. The work is held in
place by toe-clamps J and A'. The same locatmg and clamp-
ing points are used in the gaging fixture as were used in
machining the parts. These gages cover principles having a
wide application in general manufacturing work. They de-
termine accurately the relations of the milled surfaces to the
machined holes within limits that are close for work of this
kind.

INDICATING GAGES igi

Gaging Watch Escapements. — The detached fever escape-
ment is considered by horologists to be one of the most diffi-
cult parts of a watch movement to manufacture, because of
the important function it tills in the proper timing of a watch.
It transforms the rotary motion of the train of wheels into
the vibratory movement of the balance, and at the same time
acts as a brake to prevent the watch mechanism from "running
away," retarding the motion of the wheels, and imparting
the correct movement to the hands on the dial. To design
an escapement proj)erly requires not only considerable ex-
perience in this work, but also a clear understanding of the
functions that this im]M)rtant part of a watch has to fill. The
first step in producing a watch escapement is to lay it out on
paper on an enlarged scale of 50 to i, and then, by means of
certain parts outlined on tracing cloth, to study the movements
in the manner that they take place in the watch. The proper
manufacture of an escapement does not end here, and, in fact,
the most difficult work — producing the various parts cor-
rectly — is still to follow. Several methods have been adopted
in different watch-making plants to check up the machinmg
operations, in order to determine whether or not they have
been properly executed.

Projector Methods for Testing Watch Escapements. — One
method which is used to a considerable extent is to employ
a projector (an instrument designed on the principle of the
magic lantern) to project and enlarge the escapement in order
to determine if the machining operations have been correctly
done. The escapement to be projected is placed on a pane
of glass set in the frame of the projector where it is held flat
against the surface of the glass by a spring. The projector
is then placed in a dark room in such a relation to a screen
as to obtain an enlargement of the escapement of ten diam-
eters. The screen used generally consists of a sheet of drawing
paper and the outline of the projected escapement is traced
with a pencil. This sheet is then removed and the various
functions, angles, etc, of the escapement are measured on this
enlarged scale The drawing paper may be replaced by a

iga

GAGING AND INSPECTION

photographic plate and a photograph taken, but this process
requires considerable time and is seldom used.

Microscope with Illumiiiated Chamber. — Another method
consists of a microscope with an illuminated chamlxrr, mounted
in such a manner as to give an enlargement of ten diameters
and provided with a prism and a mirror, enabling the object
to be set outside the microscope in order that its projection
may be traced. The microscope is furnished with a screw,
the barrel of which is provided with loo divisions and enables
measurements to be obtained to one thousandth millimeter.
The lever escapement thus enlarged ten times with the aid
of the microscope is then analyzed. The calibrated screw is
used to check up the dimensions.

Method of Gaging Escapements employed by the South
Bend Watch Co. — A third method is that used by the South
Bend Watch Co., South Bend, Ind. This method consists in
using gages which are very accurately made for measuring
the various functions and members of a watch escapement.
While the two methods previously described would seem to
be scientific in their exactness, there b always a question in
the mind of the mechanic as to the practicability of this pro-
cedure in work of an interchangeable character. There is
little, if anything, to be gained by using methods of measure-
ment which are much more accurate and worked down to
greater degree of refinement than it is possible to obtain when
manufacturing the parts on a corrunercial basis. For instance,
by means of the microscope and illuminating chamber, it is
[wssible to obtain dimensions to within one thousandth milli-
meter. It Is practically impossible to duplicate this accuracy
on thousands of parts produced with cutters in a mechanically-
operated machine. One piece could probably be made, but
the slightest wear on the cutters would mean that' this refine-
ment would be lost. Gages can be made of sufficient accuracy
to check any variations in the work that may occur due to the
wear of cutters or improper setting. Furthermore, the gages
are at all times at hand to test the parts and determine just
how soon a slight error has crept in. If gages were not fur-

INDICATING GAGES

193

nished it would be necessary to test the parts at short inter-
vals as previously described, which would not only be im-
practicable, but would not fill the requirements of the case.

In order to make the following description of the gages clear,
reference should be made to Fig. 69 in which the various

nceg.

members of a detached lever escapement that require con-
sideration are clearly outlined. These various members are
indicated by letters, the functions and names of which are
as follows: A, escape-wheel; B, receiving pallet stone; B^,

GAGING AND INSPECnON

discharging pallet stone; C, fork; D, roller; E, impulse pin;
F, impulse face of receiving stone; Ft, impulse face of dis-
charging stone; G, locking face of receiving stone; Gi, lock-
ing face of discharging stone; H, locking corner of receiving
stone; Hi, locking comer of discharging stone; /, releasing
comer of receiving stone; /i, releasing corner- of discharging
stone; /, lift of pallet; K, circular impulse; L, drop; M, lock;
N, arc of impulse fork; 0, arc of Impulse of roller; P, im-
pulse face of escape-wheel tooth; Q, locking face of escape-
wheel toolh; R, locking corner of escape-wheel tooth; S, re-

leasing corner of escape-wheel toolh; T, locking angle of escape-
wheel tooth; and U, draft angle of pallet stone.

Each one of the functions of the detached lever escapement
must be checked after machining in order to determine if the
requirements secured by graphic methods and mathematical
calculations have been obtained. The first gage which is used
is shown in Fig. 70; the object of this is to measure the differ-
ent angles on the escape-wheel teeth. It measures the angle
that the impulse face P of the escape-wheel tooth makes with
a tangent to the periphery of the escape-wheel at the releasing
comer S\ it measures the angle that the locking face Q of the
escape-wheel tooth makes with a radial line drawn from the

INDICATING GAGES

I9S

center of the wheel to the locking corner R, and it also measures
the periphery diameter of the escape^wheel teeth. Straight-
edges B and C are used to measure the angles of the escape-
wheel teeth and are set by plugs placed in the centers of the
recesses, the radii of these plugs being the sines of the angles
to be measured. When it is staled that o.oooi inch of varia-
tion can be clearly indicated on a gage provided v^ith knife-

Elc, of Detach I

edge straightedges similar to that furnished on this gage, it
will be evident that this method of gaging is practically as exact
a method as it is possible to obtain; at least, it is accurate
enough to detect any errors in machining which would affect
the efficient working of the escapement.

The circular gage shown in Fig. 71, in which two forks A and
B arc located on pins, is used with the aid of straightedges C
and D to measure the draft angle U of the pallet stone, and also

It)6 GAGING AND INSPECTION

the angle that the impulse face of the stone makes with a line
V passing through its center. (See Fig. 69.) This gage also
measures the distance from the center of the pallet to the lock-
ing corners H and IJi and the releasing corners / and /] of the
pallet stones. In this particular case, the draft angle of the
receiving stone measures 15! degrees, and the draft angle of
the discharging stone, yj degrees.

Fig, 11. Gage tor M'

Complete AasembUd Esopement

The third circular gagu shown in Fig. 72, upon which the com-
pleted escapement is held, is used for the foUowing measure-
ments: Impulse face F and Fi of pallet stones; the drop L\ the
lock M; the arc of impulse N of the fork; the arc of impulse
O of the roller; the recoil of the escape-wheel in unlocking
the slide or run of the escape-wheel; and the side shake of the
impulse pin in the fork slot. These circular hnpulses of both
wheel teeth and stones are taken as angular measurements
from the center of the escape-wheel. The positions of the

INDICATING GAGES 197

needles A, 5, and C have a meaning only when compared with
their positions before the action of the escapement took place.
The oflSce of these needles, therefore, is to measure the angular
distance at the beginning and at the end of each action.

By the use of these three gages, all the functions of the detached
lever escapement that it is desirable to know may be measured.
An escapement can be taken from a watch and measured at every
particular point. Furthermore, these gages arc not made until
an escapement has been produced which works as efficiently as
it is possible to make it; then the various parts of the escapement
are removed and the gages made to them, ideal conditions being
realized in this way. It is also possible, by the use of these
gages, to construct a perfect working escapement from a very
much enlarged drawing with the positive assurance that it will
be an exact miniature. This latter method, from a mechartical
standpoint, would appear to be much more practical and exact
than those previously described.

CHAPTER VI
GAGING AND INSPECTING SCREW THREADS

The production of screw threads on an interchangeable basis
is one of tbe most difficult problems encountered in applying
the limit system. Considerable difference of opinion exists in
regard to the question of manufacturing tolerances on the various
elements of a screw thread, and in the following, this point, as
well as several others of importance, will be revieweti.

Elements of Screw Threads. — The elements of a screw thread
are indicated in Fig. i, and in the following paragraphs are
given the names used to define elements of screw threads:

A is the pilch diameter of a screw and is the distance between
the pitch lines, which are located where the width of the thread
and the space are the same and equal to one-half the pitch.
This element is also known as the angle diameler or the ejjective
diameter.

B is the outside diameter of a screw and b measured at right
angles to the axis. This element is also known as the/«// diame-
ler or the external diameter.

C is the smallest diameter of a screw thread and is measured
at right angles to the axis. This element is known as the root
diameler or the core diameler.

D is the pilch and is the distance between the centers of any
two adjacent threads, measured parallel with the axis of the i
screw.

£ is the included angle of the thread, measured in an ax
plane,

F is the slope of a thread,

G is the crest of the thread in the screw or nut, respectively.
This part is also known as the top and the JIal on the U. S. stand-
ard form of threads.

GAeiNO SCREW THREADS

199

E is the root of the thread in the screw or nut, respectively.
This element is also known as the boUom of the thread.

The lead of the screw is the distance that the screw travels in
a longitudinal direction when given one complete turn in a nut.

In the case of the standard V-thread, shown at ^ in Fig. 2,
there are five points to be measured in both the screw and the
nut. An error in any one of these points will, theoretically,
prevent the screw and nut from fitting together properly. In
the Cadillac form of thread, shown at B, two of these points are
eliminated, leaving only the pitch diameter, pitch, and angle of
thread to be considered on the screw and the nut.

Dixgram illuitriting Various Elements of ■ Screw Thread

^^^^Theoretically, the shape of the threads shown at C, D, and E
i m Fig. 2 present five elements that must be correct before the

I screw and nut will fit together properly. The Acme thread,

shown at F, has a clearance at the top and bottom, leaving only
' three out of the five elements to be considered. In actual prac-

tice, the U. S. standard form of thread is made with a clearance
at the top and bottom, and the chief points are to have the
thread correct on the angular faces, and the pitch and the pitch
I diameter correct. Tolerances, however, have never been gen-

erally accepted, and it is for this reason that so much uncer-
tainty exists as to tolerances that should be given on threaded
parts for various classes of work.

GACIXG AND INSPECTICW

Tolenuces on Screw Threads. — Tie three pcHots that re-
ceive the most careful atteotioD in the production of a screw
thread are the [Htch, the pitch diameter, and the an^ of the
thread. In tlie U- S. standajxl thread, errors in pitch may be
compensated for by reducing the pitch diameter by an amount

Diagiims illuBditing Various Forms of Screw Threlds

equal to about three times the pitch error. In threaded parts
that must fit well together, however, this method of obtaining
a fit is not recommended. The permissible error in pitch or
lead is dejwndent upon the length of the thread in the nut.
The longer the nut, the smaller will be the amount of error per-
missible in the lead. Another factor that must be cansidered

GAGING SCREW THREADS 20I

in fitting a screw and a nut is the angle of the thread. This
element can be compensated for by a reduction or increase of
the pitch diameter.

The Engineering Standards Committee of Great Britain has
given the subject of screw-thread tolerances considerable at-
tention, and has established certain tolerances for different
classes of fits. The formulas established for determining the
tolerances and allowances on the outside and root diameters of
the bolt and nut for the British standard Whitworth and the
British standard fine screw threads are given in the following,
and the data for the British standard Whitworth thread are also
given in Tables I and II. The tolerances and allowances on the
British standard Whitworth thread are found by the following
formulas:

Tolerance on outside diameter of bolt = —0.0035 ^ VZ^inch, (i)

Tolerance on root diameter of bolt = —0.0045 ^ '^^ ^^^ch, (2)

Tolerance between bolt and nut = +0.001 X Vz5 inch, (3)

Tolerance on outside and root diameters of nut =

+0.0035 X VD inch, (4)

in which D = nominal diameter of the thread in inches.

The positive and negative signs refer to the direction in which
the tolerance is permitted on the bolt and the nut, respectively.
The tolerance on the outside and root diameters of the nut es-
tablished by Formula (4) is to be added to the allowance given
by Formula (3).

The formulas used for determining the tolerances and allow-
ances on British standard fine threads are as follows:

Tolerance on outside diameter of bolt = —0.0025 ^ v7)inch, (5)

Tolerance on root diameter of bolt = —0.0035 x VSinch, (6)

Allowance of nut = +0.001 x y/D inch, (7)

Tolerance on outside and root diameters of nut =

+0.0025 X ^^ inch. (8)

The amount established by Formula (8) is to be added to that
obtaine^l by Formula (7).

202

GAGING AND INSPECTION

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204

GAGING AND INSPECTION

Tolerances on Pitch and Pitch Diameter. — In regard to errors
in pitch and pitch diameter, it should be understood that with an
angular thread the error in pitch manifests itself not only in the
direction of the axis of the screw, but also at right angles to the

Table IIL AUowances to Compensate for Errors in Pitch of British

Standard Whitworth Screw Threads

Nominal
Diameter,
of Screw,

Inches

H
M«
H
Me

H
H

2>.4
2H
2H
2H
2H
2li

Allowances in Pitch Diameter to Compensate for Errors in Pitch of

zho.ooos

Inch
per Inch

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

o.ooio

o.ooii

0.0013

0.0014

0.0015

0.0016

0.0018

0.0019

0.0020

0.0021

0.0023

0.0024

0.0025

0.0026

0.0028

0.0029

o . 0030

:£O.OOIO

Inch
per Inch

0.0005
0.0006
0.0008
0.0009
O.OOIO
O.OOII

0.0013
0.0014
0.0015
0.0016
0.0018
0.0019
0.0020
0.0023
0.0025
0.0028
0.0030

0.0033
0.0035

0.0038
0.0040

0.0043
0.0045

0.0048
0.0050

0.0053
0.0055

0.0058
0.0060

:kO.OOI5

Inch
per Inch

0.0008

0.0009

O.OOII

0.0013

0.0015

0.0017

0.0019

0.0021

0.0023

0.0024

0.0026

0.0028

0.0030

0.0034

0.0038

0.0041

0.0045

0.0049

0.0053

0.0056

0.0060

0.0064

0.0068

0.0071

0.0075

0.0079

0.0083

0.0086

0.0090

dbo.ooao

Inch
per Inch

O.OOIO

0.0013

0.0015

0.0018

0.0020

0.0023

0.0025

0.0028

0.0030

0.0033

0.0035

0.0038

0.0040

0.0045

0.0050

0.0055

0.0060

0.0065

0.0070

0075
0080

0085
0090
0.0095

O.OIOO

0.0105

O.OIIO

0.0II5

0.0120

o
o
o
o

:±:0.0025

Inch
per Inch

0.0013

0.0016

0.0019

0.0022

0.0025

0.0028

0.0031

0.0034

0.0038

0.0041

0.0044

0.0047

0.0050

0.0056

0.0063

0.0069

0.0075

0.0081

0.0088

0.0094

O.OIOO

0.0106

±0.0030

Inch
per Inch

0.0015
0.0019
0.0023
0.0026
0.0030
0.0034
0.0038
0.0041
0.0045
0.0049
0.0053

±o.oo3S

Inch
per Inch

0.0018
0.0022
0.0026
0.0031

axis. Therefore, if an error in pitch is tolerated, a corresponding
allowance should be made in the pitch diameter to compensate
for the transverse effect of the pitch error introduced. If the
limits for pitch diameter are determined by Formulas (11) and
(12), respectively, as given in the following, which are intended
to cover both the errors of that element and the allowance re-

GAGING SCREW THREADS

20S

lirec! to compensate for the transverse effect of pitch error,

follows that the error in pitch must be limited to such an

Lount that the corresponding allowance in pitch diameter is

greater than the tolerances given. The maximum per-

iiblc error in pitch, which as previously explained is con-

with the tolerance on the pitch diameter, is determined

by the following formulas, the thickness of the nut being-assumed

to be equal to the diameter of the bolt:

Tolerance in pitch per inch of length of thread in nut for

±0.002S

<rD

'olerance in pitch per inch of length of thread in nut for
± o.ooi 5

British standard Whitworth thread '

(9)

British standard tine screw threads =

(to)

Applying Formula (9) for a British standard Whitworth

{-inch bolt, the actual error permissible in the length of thread

in the nut will tje found to be less than ±0.001 inch.

The tolerances on the pitch diameter, which include in each

the allowances made to compensate for the maximum pitch

ir, are determined by the formulas given in the following;

Tolerance on pitch diameter of British standard Whitworth

thread = 0.005 '^^- (n)

Tolerance on pitch diameter of British standard fine threads

= 0.003 ^ZJ'. {12)

In the case of a bolt of incorrect pitch, the pitch diameter must

reduced by the amount necessary to compensate for the pitch

[Wor; that is, the pitch diameter requires an allowance for this

purpose. Thus the tolerances on the pitch diameter and pilch

are linked together, so that, if the pitch is correct, the tolerance

on the pitch diameter has the full value given in Table I, but if

the pitch is in error, the permissible limits or variations in pitch

.meter are reduced by the allowance given in Table III.

the case of a nut, the minimum pitch diameter is increased

by the allowance given in Table III. For instance, in the case

of bolts having a known pitch error, the maximum pitch diameter

given in Table I must be decreased an amount equal to that

206 GAGING .\ND INSPECTION

given in Table III, the minimum pitch diameter remaining the
same. For example, in calculating the amount of allowance
necessary in the pitch diameter for a British Whitworth i-incl
twit having, say, a pitch error of +o.ooi2 inch per inch, the
amount of compensation, as found by interpolation from Table
in, is 0.0024 inch, so tiat the limits on the pitch diameter of the
bolt arc:

Maximum pitch diameter = 0.9200 — 0.0024 = 0.9176 inch;

Minimum pitch diameter (unchanged) = 0.91 50 inch.

For a 1-inch British standard Whitworth nut having the same
litch error, the changes in the pitch diameter are:

Maximum pitch diameter (unchanged) = 0.9260 inch;

Minimum pitch diameter = 0.9210 + 0.0024 = 0.9234 inch

TaUe IV. ToIeTonces on Included Angle of Screw Tlueada (Tbe
Engineering; Standards Committee)

Foim of Thread

Nominal DamcUT,

Included AxhIc,

British Standard Whitworth Thread. . .

i H to Si.

Hto.«

( 2l(t0 3

I W to 1)1.
) J* to 3

±1.3

±05

±1 S

Tolerances for Angle of Thread. — As mentioned, the angle 0;
the thread ranks in importance with the [titch and the pitch
diameter. Errors in the angle may be such as to prevent inter-
changeability, so that it is necessary to establish limits for the
included angle of the thread. The tolerances on British stand-
ard Whitworth and British standard fine threads are given in
Table IV. Reference to this table will show that the coarser
the pitch, the smaller is the permissible error in the includec
angle.

Tolerances on U. S. Standard Screw Threads. — Severa!
concerns in the United States have adopted tolerances for their
own use, some of which have been compiled and put into con-
venient fonn. Table V gives tolerances for U. S. standard

GAGING SCREW THREADS

207

to.
f dii

^H The

iges for loose fits, and Table VI gives those for
close fits. Reference to these two tables will show that the
tolerances on the tapped hole and the tolerances on the pitch
diameter of the gage are the only two factors that are materially
changed. The louse-fit limits are, in most cases, twice the close-
it limits. It will also be noticed that the manufacturing toler-
ances on the pitch diameter of the gage are given as 0.0002 inch
'Dp to I inch in diameter and as 0.00025 i°'^li for i inch and over,
'he gage pitch diameters are made greater than the diameter
of the maximum and minimum tapped holes, so as to provide
for wear, especially on the "go" end of the gage.

Tolerances on Reference Thread Gages. — In the measure-
ment and inspection of threaded parts, even greater care is
necessary than in gaging a plain hole or shaft. The chief reason
for this is that a thread has so many elements that must be taken
into consideration that a careful study of the conditions to be
met is necessary. Master or reference screw gages should be
made much more accurately than working or inspection gages;
and owing to this fact, master t^ages, as a rule, are left soft in
order to eliminate any chance for warpage or shrinkage in
hardening.
For reference thread gages, the tolerances in pitch are generally
iven for a length of one inch, and vary from 0.0005 inch per
Inch for threads coarser than ten threads per inch, to 0.001 inch
per inch for fmer pitches. The tolerance on the pilch diameter,
as has been mentioned, is abo governed to a certain extent by
_the tolerance on the pitch. Most manufacturers, however,
ideavor to make the pitch diameter to tolerances of ±0.0001
tnch. If the error in pitch is uniform, that is, equally distributed
for the length of the thread, the tolerance on the pitch diameter
may be very small. For example, on a gage with 10 threads per
ich, the error of 0.0005 '^^^^ is distributed over ten threads,

the average error in pitch only 0.00005 inch.

The angle of the thread is one of the three elements that

affect the pitch diameter in a maimer similar to the pitch, and

where close tolerances are adhered to on the pitch diameter it is

essential that the angle be held to very close limits. The coarser

208

GAGING AND INSPECTION

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GAGING SCREW THREADS

209

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■ 2IO GAGING AND INSPECTION I

I the pitch of the thread, the smaller is the amount of error per-
I missiblc in the angle, and for thi-; element the tolerances range
I- from ± ^(f degree for the coarser pitches to ± ^ degree for the
" finer pitches.

Manufacturing Tolerances on Working and Inspection Thread
Gages. — As working and insiwctiun thread gages must be hard-
ened if satisfactory service is to be obtained from them, and as

■ they wear much faster than reference gages, greater tolerances
I are permissible. As a general rule, the pitch is held to a toler-
I ance of ±0.001 inch per inch of length, and the pitch diameter
I is governed to a certain extent by the tolerance on the work.
P When the working and inspection gages are laid out in connec-
tion with the limit system of manufacture, the tolerances per-
mitted on the "go" and "not go" ends of the gage should be
laid out with respect to the tolerances on the work. For in-
stance, the maximum or " not go " end of the plug should be
made larger than the maximum hole by an amount equal to the
maximum manufacturing tolerance permissible on the gage, and
the " go " end should be made larger than the minimum tapped
hole by an amount equal to the manufacturing tolerance per-
mitted on the gage. When the gage is new, it will not enter the
minimum tapped hole, but as a tap in most cases cuts larger than
its actual size, the gage will enter holes slightly larger than those
cut with a minimum tap. Another advantage of this practice
lies in the fact that a great amount of wear is allowed for in the
gage before it is worn too small. The manufacturing tolerances
permitted on the pitch diameter of thread gages vary from
-l-o.oooi to +0.00025 inch, depending upon the size and pitch ,
of the gage.

The tolerance on the included angle of the thread is generally
made to practically the same limits as for the reference gages.
As any variations in the included angle of the thread directly J
affect the pitch diameter, it is imperative that errors in the in- ■
eluded angle of the thread be reduced to a minimum. I

Reference Thread Gages. — Reference thread gages are made 1
either from a good grade of tool steel and left soft or from ma-
chinery steel carburized and hardened. The soft gages, when j

OAGTNG SCREW THREADS

carefully used, are more accurate than the hardened ones, owing
to the elimination of warpage or distortion, which usually takes
place during the carburizing and hardening process. Reference
thread gages of comparatively coarse pitch can be ground with
a diamond-charged lap, and when this practice is followed, the
hardened reference gage is superior to the soft one. Ordinary
lapping, however, cannot be depended upon to correct the lead
of a distorted gage; for this reason, reference thread gages are
usually left soft.

^^^^A common form of reference thread gage consists of a plug
and templet, as shown in Fig. 3. Here two forms of templets
are shown, one of rectangular and the other of circular form.
Both types are adjustable and are set to the master plug. In
manufacturing plants where the limit system is employed, these
types of reference thread gages are of little or no value, because
they cannot be used for setting the working or inspection gages,
which are not set to a standard size but provide for tolerances
on the work. In addition, a ring thread gage is of little value
in testing the thread on a screw, as it is difficult to determine
what element of the screw is in error.
In making reference screw gages for the U. S. standard form

Fig. 3. Riference Thieid GlgeE

I in maj

of thread, a flat of one-eighth the pitch is provided on the outside
diameter of the plug, whereas the bottom is made to a sharp
V-shape in order to dear fine chips and dirt that may collect in
the threads. The front end of the plug is also provided with
three angular grooves to collect dirt and dust. The crest of
the threads in the ring is made with a flat of one-eighth the pitch
and the bottom is made to a sharp V the same as in the plug.

Fig. 4 shows a group of reference gages for British Whitworth
standard threads. Ring A and plug B are left soft, and are
used for reference purposes only. The form shown at C is pro-
vided with a threaded end and a plain cylindrical end having
two shoulders, which represent the root and the outside diameter;
D and E show two reference plugs that fill the same function as
plug C. Reference gages for use in connection with the limit
system of manufacture should be made as shown in Fig. 2,
Chapter III. This enables the inspection and working gages to
be readily checked to determine when they are worn beyond
the tolerances.

GAGING SCREW THREADS 213

Pipe Threads. — There are two common forms of pipe-thread
standards in use, viz., the Briggs standard and the British
standard, as shown at A and B in Fig. 5. The Briggs standard
pipe thread is made with an angle of 60 degrees. It is slightly
roimded at the top and the bottom, so that the depth of the
thread, instead of being equal to that of a sharp V-thread (0.866
X pitch), is only four-fifths of the pitch, or equal to 0.8 -^ (num-
ber of threads per inch). The difficulty of producing a thread
with roimded top and bottom has caused a modification to be
made in the thread form, as shown in Fig. 6. Instead of round-
ing the bottom of the thread, it is made practically sharp, while
the top is slightly flattened, the flat beiiig carried down so that
it just touches what would be the rounded part of the correct
thread form. As thus modified, the formulas for the thread are:

d = 0.833 p = ^^

number of threads per inch

f-^-

26 26 X number of threads per inch

in which p = pitch of thread;

d = depth of thread;
/ = flat on top of thread.

Complete details of Briggs standard pipe threads and gage
dimensions are given in standard handbooks on machine shop
practice (see Machinery's Handbook, 5th Edition, pages 1008
and 1009).

For the length of the pipe end throughout which the screw
thread continues ** perfect," the following formula is used:

(0.8 D + 4.8) X - , (13)

in which D = outside diameter of tube, in inches;

n = number of threads per inch.

This distance is referred to as dimension F in Fig. 5. Lo-
cated back of the perfect threads is a section including two
threads having a perfect bottom and a flat top; and still farther

P"4

GAGING AND INSPECTION

' back is a portion having imperfect threads, which is formed by
the chamfer or bell-mouth in the threading die. The perfect
threads are cut on a taper equal to j inch to the foot, or ^V itich
to the inch on the diameter.

British Standard Pipe Threads. — The form of thread is that
of the Whitworth system; the sides of the thread form an
angle of 55 degrees with each other, and the top and bottom of
the threads are rounded to a radius equal to 01373 >* ibe pitch
of the thread. For taper pipe threads, the taper is J inch per

I foot, or -^ inch per inch, measured on the diameter. This

^""

1 p..>..Tj^-<«--y„„„ ,.,„._,

: 1

35fii^

J T"

-^*

— 1-r— i \ 1

rT~."r.",.,-

--f"-"i- — ' —

Fig. S' BriggB and Wbltworth Standard FormB at Pipe Threada

system has been approved by the Engineering Standards Com-
mittee as the standard pipe thread system in Great Britain, and
is known as the "British Standard Pipe Thread for Iron and
Steel Pipes and Tubes, "

In the British standard form of pipe thread shown at fi in
Fig. s, the diameter of the screw is made to such size that the
coupling or joint can be screwed on by hand to within four or
five threads of the end of the threaded portion. The length
of threads on standard pipe ends is found by the following
formula:

L = </'& - \ inch, (14)

= length of thread, in inches;

= nominal bore of pipe, in inches.

The length of the thread in the coupling or Joint should not
be made less than twice the length uf the thread on the pipe
ends, and the length of the thread at the enil of a fitting must
not be made less than the nominal length of the thread on the
corresponding end of the pipe.

Briggs Pipe Thread Gages. — The following information
relating to stantlards for Briggs pipe thread gages ha.s been ab-
stracted from the report of a Committee on the Standardization
of Pipe Threads appointed by the Amer-
ican Society of Mechanical Engineers.
The purpose of the Committee on
Standardization of Pipe Threads was
to fi.K manufacturing limits for the use
of the Briggs standard pipe thread
gages when tapping fittings or flanges,
so that pipe cut to the Briggs standard
might always enter a definite number
of turns. Although the Briggs stand-
ard is used almost universally for pipe ^'''- *" B'^kb" Kp- Tbiwd
threads in the United States, the method of its use for female
threads has not been established, in that no determinations
have ever been made of the standard depths to which hand
plug gages should enter. Tliis has resulted in mucii confusion
in the past, inasmuch as pipe threaded to the Briggs standard
is liable to vary in the number of threads it would screw into
fittings tapped at different shops. This tendency is so marked
that pipe fitting is handled in practically all cases by sending
the flanges to the shop where the pipe is cut, to be sure of
satisfactory results.

This matter is conceded to be a simple one in that all it re-
quires is an agreement among the manufacturers of fittings as
to the point at which a ring should be attached to the gage, to
establish, when the gage is inserted by hand, the proper depth
of the thread. To this end, the committee met in conference

2l6

GAGING AND INSPECTION

with representatives of the manufacturers and a,i3o of the
committee of the Society on International Standards tor Pipe
Threads. The conclusions reached were as follows:

The gages shall consist of one plug and one ring gage of each
size.

The plug gage shall be the Briggs standard pipe thread as
adopted by the manufacturers of pipe fittings and valves, and
recommended by the American Society of Mechanical En-
gineers in 1886. The plug is to have a flat or notch indicating
the distance that it shall enter the ring by hand.

Table Vn. Standard Thickness of Pipe Ring Gages

Pipe Size

•)4

Thickness A.
Inch

0.180
0.200
0.240
0.320

0.339

Pipe Size

iV4

2
2H

Thickness A,
Inch

0.400
0.420
0.420
0.436
0.682

Pipe Size

3Vi
4
4H

5
6

7
8

9
10

15
16

Thickness A,
Inches

0.766

0.821

0.844

0.87s

0.937
0.958

1 .000

1.063

1.130
1 .210
1.360
1.562
1.687
1. 812
2.000
2.125
2.250

2.375

The ring gage is to be known as the American Briggs standard
adopted by the Manufacturers' Standardization Committee in
1913, and recommended by the American Society of Mechanical
Engineers, the committee on International Standard for Pipe
Threads, and the Pratt & Whitney Co., manufacturer of gages.
The thickness of the ring is given in Table VTI. It shall be
flush with the small end of the plug. This will locate the end
of the flat on the plug flush with the large side of the ring.

GAGING SCREW THRE.\DS

217

or
ot

When using the plug gage, as shown in the illustration ac-
companying the table, the flat indicates the exact size, and the
allowable limits should be one thread large or small. When using
the ring gage, the male threads are to size when the plug gage
is flush with the small end of the ring. The allowable limits are
one thread large or small. A set of these gages to be known as
the "American Briggs Standard for Pipe Threads" is deposited
with the Bureau of Standards at Washington, D. C.

Thread Micrometers. — The simplest instrument and the
' most commonly used for measuring screw threads where
only a few are to be inspected is the micrometer caliper. In
order to use the micrometer caliper tor this work, and especially

^^the t

Fig. 7. Screw Thisad Mi

for measuring the pitch diameter and angle of thread, it is
necessary either to provide the instrument with special meas-
uring points or to make use of the wire method.

One of the many methods of measuring in the angle of the
thread is by use of the thread micrometer shown in Fig. 7.
The fixed anvil A is V-shaped, so as to fit over the thread,
while the movable point B is cone-pointed, so that it may
enter the space between any two threads. The extreme end
of the cone is removed so as not to come into contact with the
bottom of the thread. The anvil is also provided with a clear-
ance at the bottom of the V-groove so that both the anvil and
the cone-pointed spindle will come in contact only with the

2l8 GAGING AND INSPECTION

sides of the thread. When the cone point and the anvil are

in contact, the zero line on the thimble represents a line drawn

through the plane XY. If the caliper is opened, say to 0.375

inch, it means that the two planes are 0.375 inch apart. The

cone point is adapted for measuring all pitches, but the fixed

anvil is limited in its capacity, and to cover all pitches it is

necessary to provide different anvils for the various pitches. ,

To find the theoretical pitch diameter that is measured by

this micrometer, it is necessary to deduct the single depth of

the thread from the outside diameter. Expressed in a formula

for the various types of threads, the pitch diameter equals:

For sharp V- thread:

0.866

D = d-

As it is not practicable to make a V-thread theoretically
sharp, the outside will measure less than the nominal size,
the pitch diameter remaining the same.

For U. S. and A. S. M. E. standard threads:

N
For Whitworth standard thread :

0.640

D = d-

in which D = caliper reading or pitch diameter;

d = nominal outside diameter of thread;
N = number of threads per inch.

In the thread micrometer shown in Fig. 7, the oflFset of the
center line of the anvil and cone-pointed spindle necessary to
take care of the helix angle of the thread is provided for by
holding the anvil so that it is free to rotate, and by employing
various anvils for different pitches of threads. In the mi-
crometer shown in Fig. 8, the anvil is mounted in a slide and
the amount of offset is controlled by a micrometer. To meas-
ure a thread of a certain pitch, the anvil is set off center an
amount equal to one-half the pitch of the thread being measured.

GAGrXG SCRF.W THREADS

219

Micrometer having Ball Points. — The regular screw-thread
micrometer has the disadvantage of being delicately constructed
and of requiring careful and frequent adjustment. It is pref-
erable to use the standard screw-thread micrometer for ref-
erence only and to measure screw plugs or screws by means
of the standard micrometer fitted with different types of points;
a micrometer so arranged is then used to compare the thread
measured with a standard gage.

There are many types of points used; the Illustration ac-
companying Table VHI shows three. The type shown at ^4 is

I This

Fig. S. AdjuBUbte Thread Mlcrometei

made to slip over both measuring points of the micrometer,
and to obtain satisfactory results must be carefully made.
However, these points, as a rule, do not fit solidly over the anvil
and spindle of the micrometer even if they are split, and are
apt to cause errors in measurements. Better types of points
are shown at B and C. The ball point shown at B can be used
for measuring threads as fine as i5 per inch. When a thread
is finer than this, the neck becomes so small that there is not
sufficient strength, and the point is formed as shown at C
This point can be used for measuring threads as fine as 72

■\

2 20

GAGING AND INSPECTION

threads per inch. In Table VIII, the first column gives the
number of threads for which the diameter of the point has been
calculated, and the second column gives the pitches for which
this size of point can be used. These points will fit approxi-
mately halfway between the top and root of the thread in the
U. S. standard screw or threaded plug. They are used for
reference only, and are set by means of a standard screw plug.

Table Vm. Dimensions of Ball Points Used in Measuring Threads

Mackinertf

No. of

Threads

per Inch

Calculated

for

3Vi

^Vi

5
6

7
8

14
16

No. of
Threads
per Inch
Used for

3^'i

5
6

7
8-9

lO-II

12-13

14-1S
16

D. Inch

0.164

0.143
0.127

O.III

0.095
0.081
0.070
0.059
0.049
0.042
0.036

L, Inch

»62

»^

^2
^A2
H2
H2
H2
^^2

No. of

Threads

per Inch

Calculated

for

18
22

24
28

32
36
40

No. of
Threads
per Inch
Used for

18-20

22
24-26
27-30

32-34

3^38
40-46

48-60

62-72

d, Inch

0.031
0.026
0.023
0.020
0.018
0.016
0.014
O.OII
0.0086

1. Inch

^i2
Me
M.
Me
Me
Me
Me
Me
Me

They do not check the angle of the thread, as does a regular
screw-thread micrometer, but the angle may be obtained by
using different sizes of points, and comparing the size near
the root of the thread with one size of ball, using a larger ball
for the pitch diameter, and a still larger one near the top. If

GAGING SCREW THREADS

these three measurements agree with the standard gage, the
angle of thread is correct.

One-wire System of Measuring Screw Threads. — The
pitch diameter of screw threads may bt measured with an
ordinary micrometer and one wire arranged as indicated in
Fig. g. If the outside diameter of the screw is large or small,
allowance must be made for this in taking the measurement.
If the screw is oversi2e, one-half the amount that it is oversize
must be added to the dimensions obtained
by the formulas. If it is undersize, one-half
the amount that it is undersize must be de-
ducted. One wire is easier to handle than
three wires, but is not as generally used,
because the method is less accurate. This
method, however, can be used on coarse-
pitch threads where the micrometer spindle
will not reach from one thread to the next,
which is necessary with the three-wire sys-
tem. Assuming that D is the micrometer
reading over the wire when the pitch diameter
is correct, and T. P. I. represents threads per inch, the formula;
for measuring with a micrometer and one wire are:

For sharp V-thread:

^^^B For standard Whitworth thread :
^^^1 D = 1.583 X diameter of wire

Fig. 9. Diagram
iUuitiiling Ooe-
wlre System of
■nelBuriog Screw
Threads

For U. S. standard thread:

ZJ = 1.5 X diameter of wire -

r standard outside

T.P. I,

+ standard out-
side diameter.

The size of wire is governed by the pitch and form of thread.
The best size to use is about two-thirds the pitch. Mistakes
can easUy be made if too large a wire is used. A wire smaller

GAGING AND INSPECTION

than six-tenths or larger than nine-tenths the pilch should
not be used.

Thread Measuring Indicator Using One Wire. — A thread
measuring device for comparing screws with gages or working
gages with master gages is shown in Fig. lO. This device was
designed to eliminate the personal element in measuring threaded
parts or gages, as it has been found that in using thread mi-
crometers, whether equipped with conical or ball points, meas-
urements made by diilerent men, or even by the same man,

J^^ i^'^i

f?i — ft

1 b

— iilaif

UaMnrr^

FiE. .

differ at times, and show variations of as much as from 0.0001
to o,oooj inch. The same objection as mentioned in connec-
tion with Fig. 9 — that the condition of the outside diameter
of the thread is likely to affect the accuracy of the reading —
applies also to this tool,

Referring to Fig. 10, the tool consists of a block A with a
60-degrec groove in it and with a straightedge B fastened to
the top face by screws and dowels. The straightedge is so
placed that the attachment C can be adjusted to bring its
axis to line up with the axis of the thread plug being measured,
by inserting a standard measuring blod^ D. On top of block

GAGING SCREW THREADS 223

lA is another block £ which carries a . dial indicator reading
to o.oooi inch. Attachment C carries rod G, which extends
down through the slot cut in block A and rests upon a wire
H laid between the threads of the work. To prevent wire
// from dropping out, rod G is magnetized; and to prevent
the magnetism from interfering with the free movement of rod
G, the rod is surrounded by a brass bushing /, and b held from
dropping out by a set-screw, not shown. The wire H is made
of drill rod and is hardened and ground to exact size; an assort-
ment of wires is provided for the diSerent pitches of threads
to be measured. A wire having a diameter equal to two-
thirds or three-quarters of the pitch works satisfactorily, but
to facilitate calculation, it is well to use wires with diameters
in an even number of thousandths, 0.120, for instance, instead
of 0.125 inch.

If it is desired to compare a piece of threaded work with a
standard, the standard is first clamped in the block A; then a
size-block D, equal in thickness to the diameter of the stand-
ard, is inserted between attachment C and straightedge B.
Rod G is then brought to bear on a wire laid in the threads
of the standard, and the indicator spindle is brought over in
contact with rod C and a reading taken. The same process
is repeated after removing the standard and inserting the piece
to be measured; the difference between the two pieces will
then be read off on the indicator in 0.0001 inch.

This device may also be used for originating measurements
by replacing the dial indicator with a micrometer spindle,
which carries an indicating needle, thus eliminating the neces-
sity for "feel" on the part of the inspector, For originating
measurements, however, the most satisfactory way is to use a
standard measuring machine.

Three-wire Method of Measuring Screw Threads. — The
three-wire method of measuring screw threads has the advan-
tage over the one-wire method in that the outside diameter
need not enter into the calculation in order to determine the
pitch diameter. The three wires are arranged as shown at
A and B in Fig. 11. One wire is placed in the angle of the

3 24

GAGING AND INSPECTION

thread oa one side of the screw or threaded plug and the other
two on the opposite side; the measurement is taken over the
wires with a regular micrometer. The limit of this method
is reached when the. pitch of the thread is such that the mi-
crometer anvil or spindle will not reach across the two wires.

measuring Screw Threada

If the pitch diameter is correct, the micrometer readings for

the various forms of threads are:

For sharp V-thread:

D = d - r.732/> + 3(f,,
For U. S. and A. S, M. E. standard threads {A, Fig. ii):

D = d - 1.5155 ? + 3<'i.
For Whitworth standard thread (see B, Fig. 11):

D = d - 1.6008 p + 3.1657 di.
For British Association standard thread:

D = d - 1.7363 p + 3.4829 di,

GAGING SCREW THREADS

j.7S}' + ^.23(>&du

For Lowenherz thread:
D = d ~

in which

D = micrometer read-
ing over wires;
d = standard outside
diameter of screw;
di = diameter of wires;
p = pitch, in inches.

Taking the U. S. stand-
ard thread formula as an
example, assume that the
standard outside diam-
eter d is 0.5 inch. The
number of threads per
inch is 13 ; hence, the
pitch is 0.0769. The
diameter rfi of the wires
used is 0.050 inch. Then:

D = 0.500- (1,5155
X 0.0769) + 3
X 0.050
= 0.500 — 0.1166

+ 0.150 = 0.3834
+ 0.150
= 0-5334 inch.

Methods of Using
Three-wire System. —
Difficulty is sometimes
encountered in applj-ing
the three-wire system,
owing to the necessity for
retaining all three wires accurately in the grooves of the thread.
One method of overcoming this objection consists in the use
of a special stand, as shown in Fig. 12. This stand consists

IftA

226 GACmO AND INSPECTION

of a cast-iron base carrying a column to which is clamped a
micrometer head that is adjusted by a vertical screw. Directly
beneath the micrometer head, and embedded in the base, is a

gun-metal bushing holder in which is placed a scries of mag-
netized cylindrical pins arranged as shown in the plan view.
These pins prevent the wires on the anvil from rolling off and

GAGING SCREW THREADS 22?

also enable them to be accurately placed. The magnets are
arranged with their negative and positive poles as indicated.
In applying the instrument, the micrometer is adjusted until
it registers the exact si2e of the cylindrical reference gage, as
shown in Fig. 13. Then the dimensions measured over the
wires can be read off directly from the micrometer, care being
taken to see that the temperatures of the reference gage and
the gage being tested are the same.

Another simple but satisfactory method of applying the three-
wire system is shown in Fig. 14. In this case, use is made o[
the Johansson standard holder and the regular thickness blocks.

I tolen

The holder retains two carefully ground and lapped blocks,
which are spaced the required distance apart by using the reg-
ular Johansson thickness blocks. Against the face of one block
two wires of the required size are placed, and, the plug to be
measured is then brought up against these wires. A third wire
b used to test the accuracy of the work by being tried in the
grooves on the opposite side. This makes a very sensitive test,
as there is no pressure to consider except the weight of the
small wire, which is almost negligible. It is, therefore, possible
(or the inspector to detect the slightest error. The limit of
tolerance on this gage is 0.0002 inch.

GAGING AND INSPECriON

Comparison of Ball Point aad Aaril Type of Thread Mi-
crometer. — Several forms of measuring points are employed for
comparing the pitch diameters ol threaded work. Those tised

GAGING SCREW THREADS 239

in the Brown & Sharpe thread micrometer, shown at A in Fig.
15, may be used for positive measurements as well as for com-
parison. At B and C are illustrated other principles of measur-
ing, the former using a ball-point micrometer and the latter
three wires of suitable diameter, measured with the regular
micrometer caliper. The arrangements shown at A and C may
be used either for positive measurements or comparison with
other threads. The device shown at B, however, should be
used only for comparative measurements between threads of the
same form.

A recent experiment proved that the method shown at B
can only be relied upon in certain cases, even for comparative
measurements, and the same holds true of that shown at C.
The way in which this was discovered brings up an interesting
point in machine-tool construction as well as in thread measuring.
A manufacturer bought a lathe for cutting accurate threads,
which was provided with an accurate lead-screw. A serious
error, however, developed in the moundng of the machine. It
was provided with a loose thrust collar between the shoulder
of the lead-screw and the face of the bearing bracket which took
the thrust in feeding the carriage. This thrust collar was poorly
squared up, being some thousandths of an inch thicker on one
side than on the other. Unfortunately, the thrust surfaces on
the lead-screw in the bearing between which it was placed were
also poorly faced, running out sideways to an appreciable extent.
As a result, the lead-screw in revolving received an irregular
endwise movement resulting from the varying positions of the
untrue loose washer between its untrue thrust surfaces. The
machine thus cut an irregular, or drunken, thread. This fact
was brought to the attention of the makers of the machine, who
measured the lead-screw with a ball-point micrometer, and also
a sample screw cut by it, and pronounced it " O, K. " The pur-
chaser of the machine, however, brought out a measuring tool of
the type shown at A , which at once indicated varying diameters
in different parts of the threads on the work, giving evidence
of the irregularity of which he complained. The reasons for
this were evident. The ball-point micrometer shown at B

230

GAGING AND INSPECTION

measured the groove cut by the thread tool; and as this is al-
ways set at the same depth and is unvarying in shape, the error
was not detectetl. The same conditions are met with in the
three-wire method shown at C. The lower anvil of the point at
.4, however, since it spans the abnormal thread instead of making
contact with the side of the adjacent threads, indicates the
irregularity by giving an increased reading for the pitch diameter.

Fi(. 16. Siuiile Device for Teadng Lead of Taps KDd Screws

Simple Device for Testing Lead of Screw Threads. — Fig. 16

shows a simple device which is used as a comparator for testing
the lead of taps and screws. It consists of a fixed block A and
a sliding block B held in a frame as illustrated. The blocks
are provided with pointers having ball points. The sliding
block operates an indicating needle C which, on a magnlEed
scale, indicates the error in lead. The manner in which this
instrument is used is as follows: The position of the pointer on
the scale is noted when the instrument is brought in contact
with a standard plug that engages the ball pwints; the free block
B adjusts itself to the thread into which its point enters aiid

carries with it the needle C. Next the tap or screw to be tested
is placed in position against the device. If the lead of the
screw or tap is correct, that is, if it is the same as the standard,
the pointer wiL occupy the same position on the scale as it did
when brought in contact with the plug. If the tap or screw is
long or short in lead, the pointer will show the amount by its
movement either to the right or to the left. The circular arc
of the scale is generally graduated to read to 0.001 inch.

i^r-feylLj

Fig. 17. ladiciting Compuatai lor Tes

i Tapg ■

Indicating Comparator for Testing Lead of Taps and Screws. —

A somewhat more elaborate device for testing the error in lead
of taps and screws is shown in Fig. 17. In this, one ball point
A is fixed and is mounted in slide 5, which is operated by a
knurled-head screw C. This ball point A may be screwed into
any of the holes D which may be located \ inch apart. The
other ball point E is inserted in a movable block F mounted on
ball bearings. This block is connected, through lever C, with

332

GAGING AND INSPECTION

the indicator or sensitive gage H, which is so arranged and
graduated that each thousandth of an inch can be easily read.
When the standard plug b placed against the device, the ball
points enter between threads the same as in the device pre-
viously described, and slide B is adjusted by the knurled-head
screw C so that the indicator points to zfro. When the screw

Pig. l8. Wella Bros. Ripid Screw and Tsp Le«<l Tetler

or tap to be tested is placed against the bait points, any error
will then be apparent by the motion of the needle.

Wells Indicator for Testing Lead of Screws and Taps. — A
simple but effective device for testing the lead of screws and
taps is shown in Figs, i8 and 19. This device is made by the
Greenfield Tap & Die Corporation, Greenfield. Mass., and, as
shown in Fig. 18, comprises a base carrying one fixed and one

GAGING SCREW THREADS 233

movable pointer. These pointers are made to enter the threads
of the screw, as shown in Fig. 19, the indicator previously having
been set to zero by means of a reference plug. In using this
device, the screw is simply pressed against the points and any
deviation from the correct lead is shown by ihe indicator in
thousandths of an inch. A set of steel blocks furnished will
this device permits of the rapid testing of any size of screw
The blocks vary in thickness, thus enabling the screw to be place(

so that the points will
come in the center or
on the axis of thc
screw. The points arc
removable to cnablo
them to be replaccii
when worn.

Wolfe Dial Indica-
tor for Testing Lead
of Taps. — A dial in-
dicator known as the
Wolfe indicator, whi.h
is parti cularjyadapud
for testing the lead ul
taps, is shown in Yi^.
20. It can be used
for testing any screw
or tap having a length

r '

* r

Illl

TTTm

of one inch or more,
and an accuracy of
0.CXX12 inch is said to
be easily obtained. Th
read to thousandths of
on each side of the zere
points A and B, whic
thread to be tested; po
ary. Point B can be u
into the socket K when

Fig. 19. Indicator shovn in Fig. 18 la Use teit-
ing Lead of Screw

e dial of the indicator is graduated tc
an inch and has a range of o.o;4 incl
mark. This instrument has two bai
1 are brought into contact with th
nt A is movable and point B station
nscrewed from its socket and screwec
a testing range of one inch is desired

^^^^^^^^^^^^^^^^^H

pa34

GAGING AND MSPECTJON

Point B is held in a sleeve C that can be adjusted by screw D,
the sleeve being held in position by clamping screw E. The
loop or handle G is used for holding the indicator. In addition
to the indicator proper, a centering gage provides a means
for enabling taps, screws, etc., to be tested on the center line,
thereby insuring the required accuracy. This centering gage
can be used on taper as well as straight taps and has a
capacity for diameters ranging from J to ij inch. The adjust-
able points on the centering gage are graduated in thirty-

seconds of an inch, and they may be held in position by
thumb-screws L.

As the illustration shows, this centering gage also has a main
plate J against which the piece being tested is held. When
using the centering gage, the graduated points are set out from
the plate J a distance equal to the radius of the tap or screw
to be tested. Thumb-screws L are then tightened, thus holding
the points in the adjusted position. The tap or screw is next
placed in the centering gage and is held down on plate / and
against the points. l"he indicator is held in the hand with the
second finger through the loop G. The gage is brought up so

GAGING SCREW THREADS

235

that the stationary ball point B enters the thread and rests on
the flat end of point /. The movable point A enters the thread
and rests on the flat part of the point IJ. The indicator will
then show whether the thread is " long " or " short " in thou-
sandths of an inch. If the thread is accurate, the needle will
remain at zero. If it is " long," the pointer will move in the
direction of F; and if " short," it will move in the opposite
direction.

Lead Test Indicator. —
Figs. 31 and 22 show a
thread test indicator used
in the Pennsylvania Rail-
road shops for testing
staybolts, taps, and lead-
screws. This instrument
comprises a standard on
which is pivoted a sensi-
tive spring pointer // and
a stationary pointer J.
The latter is mounted on
a bar A' which may be
adjusted minutely length-
wise by screw L. The
indications of pointer //
are read on segment .1/,
the support of which may
be adjusted, through the circular dovetail slot, about the center
of the pivot of // to bring the reading to zero. This adjust-
ment is effected by the screw N and clamped by screw
Spring stop-screws P limit the extreme movement of the needle.
When in use, the points are adjusted to span a certain number
of threads and the instrument is pushed against the screw to be
measured until the measuring points are firmly pressed into the
thread. Scale M is then adjusted until the indicator points to
zero. The instrument is then moved from one place to another
along the thread and, if the needle points to zero in all positions,
the thread is uniform.

236 GACFNG AND INSPECTIOM ^|

ij ii n -^. e ^ ^.' en ^H

^^^■sl^'^s^ ■

y j^^^^^^^^^^E

iS.t; '^ E -« 9=^ ^ a ■

^fln^l

indicating poin
provided to su
of threads. An
. 22. Various
rements are also
ngths for carryii
hown at JT, an
s the instrument
tion, since base

r\g yi^B^^^B

The

hapes
n Fig
measu
ous Ic
are s
make
pplica:

.a"-«.'S2B" ^

3 -i ^ [10_ ^H

Ik«^I

i^^i

III hill I

■

Indicator

r the p
s. and V
;rent piti
is show
■ws for CO
R. and b
d indical
; whole a
lly univi

Test

nea
ball

set

sere
at .
fixe.
The

tica

■

■^

Fig. sj. Lead

ig the amount
shorter than
dicator is first
own accuracy;
in place and
oints along its
w whether the
; indicator can
f thread at or

ftgjjg^

^ 5-2^5 ^ia « ■

HQ^kj^H^^H

^ s^ "■i-i'^l ■

^^^^^l^^l ^^^1

= ^ - * S -5 1 M o ■

' [^1

his tool is i
;ads are !o
y this test,
■erence sere'
ested is th
taken at v;
ngs on the •
t, or regula
easuring th

'>^^^^^^^H

Another use of t
by which the thn
the true pitch. B
set to zero on a rel
the screw to be t
measurements are
length. The readi
pitch is long, shor
also be used for m

^ i. — ^^^^^^^^1

GAGING SCREW THREADS

' be used and the (

337

ly length may be used and the centers or yokes fastened

lem at the points required.
Bickaell-Thomas Thread Lead Indicator. — The tool shown in
Figs. 23 and 24 is a simple device for testing the lead of both
external and internal screw threads. When in use, the tool is
held in one hand, preferably the left, and the screw is pressed
against the two points, which are spaced \, \,qx i inch apart, as
desired. If the lead of the thread is normal, the indicator

Fis. 13. Thread Lead lodici

External Thread

needle will register zero; if the lead is short, the needle will show
on the minus side; if long, on the plus side. Each line of the
graduation represents 0.001 inch. The " table " on which the
screw rests in testing is adjustable to accommodate screws of
any diameter. For internal measuring, the table is removed
by loosening the thumb-screw and drawing it off. The end of
the instrument containing the point is small enough so that
tapped holes as small as \ inch in diameter can be tested. This

330

is a feature which is of the utmost importance in making sure
that the lead of the threads on both the screw and in the tapped
hole are the same. A master is furnished with each gage so
that the operator may be sure at all times that the needle point
is at zero when the gaging points are spaced correctly.

Testing Angle of Thread. — Fig. 25 shows a simple device for
testing the angle of a thread. This consists of a special base
carrjing two center supports, and a rear support or slide for
holding cone-pointed inspection rods.

The procedure followed in using this device is to place the
plug to be inspected on the centers, and then locate one of the

iDlemaJ Thread

cone-jjointed rods with the carefully ground and lapped point
in the space between the threads. A sheet of while paper, for
illuminating purposes, is then jilaced on the base, as shown, and
the thread viewed through the magnifjing glass. If it is desired
to determine just how much the angle is off, rods having points
ground to included angles of 60^ or 59^ degrees are used, the
angle depending upon the pitch of the thread and the tolerances
permitted. Usually, however, the thread is tested for " hght,"
and if the cone point does not bear evenly on the angular sides,
the thread is not passed. By using the two points, which are
spaced exactly i inch apart, it is also possible to test the lead
with this device.

GAGING SCREW THREADS

239

Limit Working and Inspection Thread Gages. — Most uf the
devices described in the foregoing are somewhat limited in their
application and will not be found suitable when a large number of
threaded parts are to be produced within certain limits of toler-
ances. As a general rule, manufacturing gages are designed to
handle one diameter and pitch of thread. The most common
form of limit thread gage is shown in Fig. 26. For threaded

►les, a limit plug gage A having two threaded ends, one of
which is made to enter the hole and the other not to enter (when
the work is satisfactory) is used. For external threads, such as
screws, etc., a templet, as shown at B, having " go " and " not
go " holes is used; or, for the larger sizes, two rings, as shown
at C, may be employed. The chief objection to these gages is
that they do not indicate what element of the thread is in error.
For many classes of work, however, they fill all requirements,
especially when the necessary care is exercised in producing the

r 240

GAGING AND INSPECTION

tools used in cutting the threads. The general practice is to

I use the double-end templet B for sizes up to one inch in diameter;

the " go " end is knurled. For sizes over one inch, two rings, as

Plug and Templet

shown at C, are used. These gages are adjusted to the plug A.
For inspecting the U. S. standard thread, the threads in the ring
and plug have flat lops ^ one-eighth the pitch — and sharp

ilk

1te

^^-M

Fig. 2

Double-end Limit Plug Gage hsviag Beveled Shoulder
for Inspecting Cfaunfered Thretd Bale

V-bottoms to clear line chips, dust, and dirt, and also to insure a
bearing upon the angular sides of the thread.

In cases where the threaded bushings, sockets, etc.. are made
with a chamfered mouth, the " go " end of the plug gage, as

CAGING SCREW THREADS 241

shown in Fig. 27, is made with an enlarged shoulder, the front
face of which is beveled to the angle required. This shoulder
is then cut away, as shown at /I , to provide a means for inspecting
the accuracy of the angle. The threaded part has three grooves
to collect fine chips and dirt.

Limit Snap and Plug Gages for Threaded Work. — A
limit snap gage for threaded work, which is manufactured by
the Greenfield Tap & Die Corporation, is shown at A in Fig.
28. This gage is used for testing the pitch diameter of screw
threads, and is prvividcd with hank'nal cone [wints, carefully

Fig. i3. Limit Saap Gage aod Selling Plugs

ground to the angle of the tliread wall. The points are not
placed directly opposite each other, but are offset an amount
equal to one-half the pitch. The cone points are adjustable
and are set by locking screws, which are sealed by the inspec-
tor after he has checked the gage; B shows a setting plug that
is similar to the plug shown at A in Fig. 26, and is used for
sizes up to J inch; C is used as a setting plug for sizes from
J up to 3 inches; and D for sizes from 3 inches up.

Fig. 29 shows the snap gage illustrated at A in Fig. 28, held
in a stand and used for the rapid inspection of screw threads.
This illustration shows clearly the application of this gage.

343

GAGING AND INSPECTION

At A, the screw being tested is too small and has passed both
sets of points; at B, the screw is too large and will not pass
the upper or "go" points; while at C, the screw is just right,
as it has passed the upper [wints and is hanging on the lower
ones.

Limit Snap Gages for Testing Lead and Pitch Diameter. —
While the cone points in the gage shown at A in Fig. 28 are
set off an amount equal to one-half the pitch, they do not
cover a sufficient number of threads to detect errors in lead.
A modification of this gage is shown in Fig. 30. This is pro-

Fig. 19. Snap Cm* Bhown in Kf. 28

InspectinE Scrsw Threads

vided with two sets of three points, making six cone points in
all. The points held in the lower jaw of the gage are spaced
approximately ^ inch apart, depending upon the pitch of the
thread, and the upper points are offset an amount equal to
one-half the pitch. By the use of this gage it is possible to
detect errors in lead which would prevent the screw and nut
from fitting together as they should.

Another gage of the snap type, which inspects both the lead
and the pitch diameter of a screw thread is shown in Fig. 31.
This gage comprises a frame carrying three conical points
B, C, and E, which are accurately ground to the required angle;

GAGING SCREW THREADS

243

the extreme ends of the points are removed so that the points
will come in contact with the sides of the thread. Points
B and C are fixed in the lower jaw of the gage, so that their

TTT

•'..II

Maekinerff

Fig. 30. limit SnAp Gage for Testing Lead and Pitch Diameter

center distance is equal to the distance between a number
of threads representing twice the length of a nut of correspond-
ing diameter. The third point E is held in the upper jaw
and is midway between the lower points. All three are set

\ ....M. /

SCREW OR PLUG

j_^

:^^^^.

V^-^''

:^^

T=e

Machinery

Fig. 31. Another Limit Snap Gage for Testing Lead and

Pitch Diameter

to a known standard. Located opposite the point £ is a point
F having a flat face Ay which is adjusted so that the small
cylinder D (which is of such diameter that it will touch the
sides of the thread halfway down its depth) will just enter
the thread of the screw when made to the minimum pitch

TPI

r\X, -,-,■

Sm^MS

4tt

GAGING SCREW THREADS

245

diameter. In testing, if the screw enters between the points,
and the "not go" plug D does not, the screw is within the
required limits for pitch diameter; any error in pitch is com-
pensated for by tJie necessary reduction in pitch diameter.

Indicating Gage for Inspecting Lead and Pitch Diameter. —
When the volume of work to be insi>ected warrants the ad-
ditional expense, an indicating gage is to be preferred to one
of the rigid snap type. A satisfactory indicating gage for
testing the lead and pitch diameter of screws is shown in Fig.
32. This gage comprises a cast-iron base A to which is attached

Fig. 33. Fixture (oi Testing Lead of Opening Die Chueii

a fixed jaw B; the movable jaw C is attached to a slide D.
Jaws B and C are each provided with two carefully ground
and lapped V-projections, which fit in the threads of the screw
being tested. The extreme ends of the points are removed,
so that the projections will come in contact with the sides of
the threads. The projections on blocks B and C are located
exactly i inch apart and one set of points is offset from the
other an amount equal to one-half the pitch of the thread
being inspected. Slide D is kept In the forward position by
an open-wound spring, and block C is withdrawn from contact

246 GAGING AND INSPECTION

with the work by handle E. Thus the pressure on the work
being tested is that exerted by the spring that holds the slide in
the forward position. When being inspected, the work is placed
on the hardened and ground block F. The indicating mechanism
comprises two levers G
and H. The short end
of lever G comes in con-
tact with the flattened
face of a plug I on slide
D. Lever E is fulcrumed
at point / and is kept
in contact with the long
arm of lever C by a spring
K. The ratio of the two
levers, or the mulliplica-
don of the error, is 50 to
I, so that the marks on
scale L (which are spaced
0.050 inch apart) repre-
sent an error in the
diameter of the work of
0.001 inch. With this
device, it is easy, there-
fore, to detect errors as
fine as 0.00025 inch, al-
though for the average
run of work this degree
of refinement is consid-
ered unnecessary.
Inspecting Die -Chasers. — The extensive use of opening
die-heads for the production, in large quantities, of commer-
cially accurate screws has necessitated, in many plants, the
use of fixtures for inspecting the chasers, in order to insure
that the pitch is within the desired degree of tolerance; also,
in straight chasers, that the threaded face is correct in relation
to the rear face. One simple but effective device for testing
the lead of die chasers is shown in Fig. 33. This fixture was

GAGING SCREW THREADS 247

Kigned for testing the lead and registration of Geometric
and Modern die chasers. It consists of a base carrying several
slides that give the required movement, and an indicator for
testing the chaser. A chart is prepared for checking the regis-
tration of the starting teeth on the chaser.

The chaser is located by the same slot that locates it in the
die-head and, as shown in the illustration, is held in place by
a spring plunger pressing upon it an at angle of 45 degrees.
The top slide is located by a pointer which is held on a bracket
and meshes with one tooth of the chaser. The spindle of the
dial indicator bears against the end of this slide. To test

the chasers, No. i is set at zero on the dial indicator, and then
the chart is used to determine if the other chasers are correct
in relation to the first by noting the position of the needle on
the indicator as each chaser is put in place.

Fig. 34 shows a fixture for testing the straightness of Geo-
metric and Modern tiie chasers. In this case, the chaser is also
mountefl on a slide, and a pointer, in connection with a multi-
plying lever, is used to indicate the distance from the rear
face or slot to the pitch line of the chasers. The slide is ad-
justed to bring each tooth successively in line with the pointer,
and then the movement of the indicating lever is noted. This
lever is kept in contact with the slide so that any change in
the position of the slide for the various teeth in the chaser is
multiplied by the indicator. The lower slide is adjusted to

GAGINQ AND INSPECTION

bring the pointer in line witii the various teeth of the chaser
while they are being tested.

A. S. M. E. Gaging Devices. — In Figs. 35 to 42, inclusive,
are shown the gaging devices considered by the sub-conunittee
on gaging systems of the American Society of Mechanical
Engineers, in its effort to find a gage that will quickly measure
variations in both
lead and diameter.
The devices shown in
Figs- 35- 36. and 39
are suitable for a wide
range of diameters
and pitches; the other
gages are limited to
one size of screw or
tap.

^ The gage shown in
Fig. 35 measures the
variation from stand-
ard of both the pitch
diameter and the lead
of screws and taps.
It is constructed with
the fixed V-point, a
micrometer adjusted
grooved roll, and a
floating point. The
grooved roll fits over
the thread and is free to move sideways to allow for variation
in lead. The roll is set to the standard pitch diameter of the
work to be tested by the micrometer thimble. A floating point
is so connected that the longer lever shows variations in lead,
and the shorter, variations in pitch diameter. The work is
placed between the points, as shown in dotted lines, and the
variations from standard pitch diameter and lead are read
directly in thousandths of an inch.

The gages shown in Figs. 36 and 37 are to be used together.

GAGING SCREW THREADS

That shown in Fig. 36 measures variations in pitch diameter
only. The V-shaped anvil is adjustable through a wide range

Fis. 38. S^t Gage for Haaniring Pilch Dlamatar*

of diameters and can be locked ia position by a clamping
screw. The gaging arm is pivoted, and the gaging pomt is
held in contact with the work at a constant pressure by a

2 so

GAGING AND INSPECTION

spring at the rear. A dial indicator is in contact with the arm.
The gage is set to a standard, and as the work is passed be-
tween the points, variations in diameter are transmitted through

Fig. 39. Combination Gage for Measuring Pitch Diameter

and Lead

Fig. 40. Gage having Two Fixed Points

the arm to the dial indicator, where the amount of variation
may be read directly in thousandths of an inch.
The gage shown in Fig. 37 is for testing the lead only. The

GAGING SCREW THREADS

251

I positive point may be used in any of four positions to allow
for different lengths of thread. The floating point is part
of the bellcrank lever, which is mounted to act on the dial
indicator as the distance between the measuring points varies.
After the indicator is set to a standard, the work is positioned
on the two points. Any variation from the standard in the
lead may be read directly, in thousandths of an inch, on the
dial.
In Fig. 38 is shown a gage that can be used for pitch diam-

I eters only. It is made slightly tajjering and is split and fur-

Combination Gage with Hinged Joint

nishcd with screws for adjusting and locking. It is adjusted
so that the setting standard A will screw into the gage until
a line on the standard matches a line on the gage. The other
lines on the gage indicate o.ooi inch variation from the stand-
ard in pitch diameter.

A combination gage for pitch diameter and lead is shown
in f 'g- 39- In this gage there is a fixed point, and two adjust-
able points, one for variations in pitch diameter and the other
for variations in lead. The errors, in both cases, arc read in
thousandths of an inch on the dial indicators. The indicators
must be set to a standard before testing work. An adjustable

as*

GAGING AND mSPECTION

I block may be set by a vernier so that work resting on it vnU
[have its center line in line with the gaging points.

In Fig. 40 is shown a gage with two lixed points, located
' correctly. Guiding grooves serve to align the work, which
is placed in the gage as shown by the dotted lines. The amount
of variation from the standard can only be estimated. A
gage fitted with a hinge F and spring G, like that on a spring
caliper, is shown in Fig. 41. The jaws are opened when the
screw to be measured is inserted, and are brought together
by the fingers. The
hole B is the "go"
gage. It has a stand-
ard thread, and, when
the fiat surfaces be-
tween this hole and
the end are in con-
tact, any screw that
goes in will enter the
tapped hole, regard-
less of the lead error.
The other three holes
C, D, and E are
"not go" gages and
test the root diameter,
pitch diameter, and
outside diameter, respectively. In order to eliminate the ques-
tion of lead, in both C and D, only a single turn of thread of
special form, as shown by the enlarged views, is used. The last
hole F is plain, to gage the minimum outside diameter. The
"not go" gage D, in combination with the "go" gage B, limits
errors of pitch diameter and lead also.

The gage shown in Fig. 42 is similar in principle to that
shown in Fig. 40. It has four fixed points located in the cor-
rect relation to one another. Screws locate the work so that
its center line is on the line of the gage points; when the work
is placed in position, variations in lead and pitch diameter
may be estimated.

Fi«. 43.

GAGING SCREW THREADS

aS3

Projection Method of Measuring Screw Threads. — A
method uf inspecting screw threads which, up to the present
time, has not been extensively applied, but which for certain
purposes (especially laboratory use) can be used with success,
is the projection method. This consists chiefly in comparing
a screw gage to be tested with a carefully drawn diagram
magnified about fifty times. The gage to be tested is mounted
on a suitable fixture, and is then illuminated by the aid of a
small arc lamp and condenser. Carefully arranged lenses arc
then used to throw a magnified image of the thread on the
chart or screen, and observations are made on the diagram.

The lenses should be chosen to produce a uniform inumiHii h
tion over the entire field, and distortion should Iw t'liniltinlrd
A& the screen carries a diagram of the thread wlili It l» iruiij
nificd fifty times, it is an easy matter, as Hhowi) In |'|(( *\,
to compare the image projected with the corrcil \Utfnji |tfi||||)i
In Fig. 43, the image has been lowered simiirwitii) Ut IftifMiiMi
the depth of the shadow, and it can Ik- ncrn titiil i\ni llin-iul
on the gage is comparatively rough iind imofmily tntmii In
places. Another method of compiirison U Ut ^iljuil, ^Uml^
taneously, the image of an accurate mtoW |iIium| |««.«Mi' tlw
one to be examined; the difference lirlwn' '' ■ .
detected. This method applicM to iimlr K"1"
as it c^'idently would be ini|>0NMb]e lo pf,,.< , .
ring gage or nut in this manner.

CHAPTER VII

GAGIITG AND INSPECTIHG GEARS

Geaks are inspected during the process of manufacture to
determine if the shape, diameter, width, tooth forms, etc.,
are correct within the required tolerances, and they are also
tested for concentricity. Gears in which the teeth are not
concentric with the hole,
or are unevenly spaced,
are noisy, especially when
they are operated at high
speeds. The teeth, there-
fore, receive the most
careful attention in the
inspection department.
The tooth shape, pitch,
and pitch diameter are
the three most important
ix»inls to consider.

Inspecting Gear Blanks.
— The methods of test-
ing blanks for spur gears
do not differ from those
testing many other
interchangeable parts, in
which plug gages, snap
gages, and regular mi-
crometer calipers are used. For inspecting bevel gear blanks,
these tools are employed in connection with properly shaped
templets. The type of inspection tool is governed to a large
extent by the character and shape of the work. An impor-
tant point in machining blanks for spur gears is to have the
sides &nisbed accurately in relation to the hole, so that the

Uar*

nrriF

GAGFNG GEARS

255

arbor on which the gears are held, especially when several
are mounted together, will not be sprung out of truth. A
satisfactory means of testing this is to place the gear blank
on an accurate arbor held on centers, and rotate it past the
spindle point of a dial test indicator.

Templets for Bevel Gftar Blanks. — Bevel gear blanks re-
quire some form of templet Cor testing the relation of the angular
faces to the hole and to each other. One form of templet gage
for bevel gear blanks is shown in Fig. i. This gage comprises

Templet for Inipecting Miter Gaar Blanka

a central plug which fits in the hole in the gear blank, and a
templet fitting in a notch cut in the plug. This notch is cut
to the center so that the flat gaging face of the templet and the
axis of the plug coincide. With this device, it is possible to
test the truth of the hole with relation to the angular face of
the gear, and at the same time inspect the angle of the face.

A convenient form of bevel gear templet is shown in Fig. a.
This is made of sheet steel, and completely encloses the gear,
thus controlling both the angular face and the over-all length.
In laying out this form of templet, the first step is to find the
center of a circle which will touch all three sides of the isosceles

256 GAGINC. AND INSPECTION

triangle, as shown by the dotted outline, This is a simple
problem in trigonometry, as is shown by the illustration.

Bevel Protractor for Testing Bevel Gear Blanks. — The
ordinary bevel protractor familiar to all mechanics is com-
morjy used for testing bevel gear blanks. A special appli-
cation of this principle is shown in Fig. 3. This device consists
of two hinged bases carrying sliding blocks, in which studs
are held for supporting the gear blanks being tested. In addi-
tion to having regular protractor graduations for setting the
gear axes to the required angle, graduations are provided for

i r

-pp^

s||:

^.r. :^ A, : _. ::;:. ::^-'^^^

(»"-.

Tig. 3. FrotractOT for T«8tiiiK Tnith of Bevel Gens

showing the longitudinal settings of the sliding blocks on the
two arms. These longitudinal graduations, however, cannot
be used to advantage as a measurement of the center distances
of bevel gears, but by swinging the movable arm back to 1
included angle of 180 degrees, the device could be used for
spur gears. As the angular face of a bevel or miter gear is of
prime importance, two blanks could be held in this fixture
and rotated together, to test for concentricity and correctness
of angular face.

Gear Tooth Templets. — The simplest form of gear tooth
templet is shown at A in Fig. 4. This is a piece of sheet steel
with a slot in its lower end equal in width to the thickness

GAGING GEARS

257

of the tooth at the pitch line and of a depth equal to the height
of the tooth from the pitch line. The chief objection to this
templet is that it wears quickly#at the sharp comers a and soon
becomes inaccurate; B shows a form of templet which is used
chiefly for bevel gears and is more like a scriber than a templet.
It is used to scribe a line on a gear indicating the depth to which
the teeth are to be cut at the rear or large end. It is used only
when a few gears of one size are to be made.

Gear Tooth Caliper. — The gear tooth caliper shown in Figs.
5 and 6 is a widely used tool in the shop for measuring gear teeth,

PITCH UNE

^-^~^^^:-<v^V;^.v>.

^v^l

llarkinrrp

Fig. 4. Templets used in cutting Gear Teeth

especially after cutting the first tooth. This test is especially
desirable if there is any doubt about the accuracy of the blank
diameter. (The outside diameter of a gear blank can be found
by adding 2 to the number of teeth and dividing by the diame-
tral pitch.) To test the tooth thickness, two trial cuts are taken
for a short distance at one side of the blank until a full tooth is
produced. The vertical scale of the caliper is set so that when
it rests on the top of the tooth, as shown in Fig. 6, the lower ends
of the caliper jaws will come to the pitch circle. The horizontal
scale then shows the chordal thickness of the tooth at this point.
When a gear tooth is measured with this caliper, the chordal
thickness T (see detail of the tooth) is obtained, and not the

258 GAGING AND INSPECTION

thickness along the pitch circle. Hence, when measuring teeth |
of coarse pitch, especially if the diameter of the gear is small,
dimen^on T should be obtained. It is also necessary to find

the height x of the arc and add it to the addendum S to obtain J

the correct height //, in order to measure the chordal thickness!

T at the proper point on the sides of the tooth.

If a = one-half the angle subtended from the center of t

GAGING GEARS

259

gear by one gear tooth (see Fig. 6); N = number of teeth in
gear; T = chordal thickness of tooth at pitch line; and R =
pitch radius of gear, then:

a = 90 degrees -5- N; T = 2i? x sin a.

The height x of the arc equals i minus the cosine of angle a
multiplied by the pitch radius of the gear, or expressed as a

Jiaekiner§

Fig. 6. Diagram iUuBtrating Calculation necessary to determine
Thickness of Tooth with Caliper shown in Fig. 5

formula, x = R{i — cos a). The vertical scale is, therefore,
set to the dimension H, or x + addendum S.

Tolerances for Spur Gears. — The three most important
factors in a gear are the profile of the teeth, pitch diameter, and
center distances. The outside diameter is not so important, as
there is always clearance provided at the bottom of the teeth.
The limits of accuracy should be based on the pitch, and the

260 GAGING AND INSPECTION

accompanying table gives the limits for gears from 16 to 4
diametral pitch. The tolerance on the shape of the teeth, whea
they are of the involute form 'depends upon several factors. In
the first place, if the gears are to transmit a heavy load at com-
paratively high speeds, and the noise is to be reduced to a mini-
mum, the tooth curves must be as accurate as it is commercially
possible to make them. On the other hand, if the gears are to
run at slow speeds and noise is not objectionable, much wider
Umits are permissible. For the average run of good gears, es-
pecially for automobile transmissions, an endeavor is made to
hold the involute curve to a tolerance of 0.0005 ttich. The
variation in tooth spacing should not exceed 0.002 inch if the
best results are to be expected. Gears having ground teeth,
however, are made to closer limits than this for spacing, usually
0.0005 inch.

M»nuf«cturine Limits for Spur Gears

Pilch

Caita
Distance

Pilch DinmrlH-

Outside Diai

ncUT BUalB

±0.001

-0,00,1

to -0 005

0.000 to

-0.005

■4

±0,003

004

000 U

ooS

006

±0 005

to -0

009

000 tc

007

±0.006

008

-0.009

tn -0 OI3

000 to

-0

oiS

Tolerances for Bevel Gears. — In mounting a bevel pinion
which must run in proper mesh with a ring gear, it is essential
that backlash be provided for to prevent crowding the teeth.
The apex angles of the pinion and ring gear are frequently made
to a tolerance as close as 0.005 inch. For gears that are hardened,
however, it is necessary, in some cases, to allow a greater toler-
ance than this to take care of warpage which causes a change
of the angle of the bevel gear. When this is done, it is usual to
allow for a reasonable amount of backlash between the teeth,
the limits varying from 0.005 t-o 0007 inch, but never exceeding j

GAGING GEARS

26i

O.OIO inch. This means that a bevel gear must be straightened
before being assembled if the warpage is in excess of the amount
given; otherwise, it will be noisy and inefficient.

The tolerances on the teeth of bevel gears are dependent upon
the uses to which the gears are to be put. Generally, the tooth
curves are made to within 0.002 inch and the spacing of tlie
teeth to the same tolerance. As previously mentioned, however,
when a gear is hardened, the tolerance, of necessity, must be
greater than this to provide for warpage of the teeth. Bevel
gears of the Straight- tooth type, when used in automobile trans-

Fig- ?• Sp«citl Plug Gtge ror Gagiag Gear Cen

missions, are generally run in, using emery and oil to grind down
any slight irregularities in the teeth due to warpage in hardening.

Testing Center Distances of Spur Gears. — As mentioned, the
center distances of spur gears which must run quietly is an im-
portant consideration in the cutting of gear teeth. Fig. 7 shows
a simple but effective gage for testing the center distances of
spur gears. The gage consists chiefly of two accurately ground
collars B and C, which are held on plug gages D and E, as shown,
the latter being provided with bushings to suit the diameters of
the boles in the gears. Collar B is ground very slightly ec-
centric, and the eccentricity is graduated on the collar.

To illustrate the use of this tool, assume that the center dis-
tance A is 5 inches. The collars B and C are made so that the

I of their combined radii will equal this amount,
words, collar B could be 2 inches and C S inches in diameter.
Referring to Fig. 8, which shows the angular spacing for variations
in the center distance of the gears, assume that F represents the
zero or datum line from which the center distances are measured.
If the graduated collar B is turned through an angle of 36 degrees
51 minutes in a clockwise direction, the center distance will
equal +0.001 inch. Similarly, if collar B is turned the same
amount in a counter-clockwise direction, the center distance

—0.006"

1 "-

ifi

Enlarged View at Graduated Disk B shown li

will be — o.ooi inch. If the collar is rotated through an angle of
90 degrees in either direction, the center distance will be +0.005
or -0.005 ii"^^'' depending upon the direction in which the
collar is turned. By making a series of plain collars to replace
collar C, any required center distance may be measured to very
accurate limits by using the same graduated eccentric collar B.
Testing Pitch Diameter and Concentricity of Spur Gears. —
Many interesting fixtures have been devised for testing the
pitch diameter, center distance, and concentricity of spur
gears. A standard fixture used for this purpose which is built
by the Morse Twist Drill & Machine Co. is shown in Fig. g.

GAGINO GEARS 263

This fixture consists principally of a base carrj-ing one fixed
and one movable slide, each slide carrying a stud on which
are held the gears to be tested. The gear held on the stud

■nd Concentricity

'in the fixed slide is usually a carefully cut, and sometimes
ground, master gear, which is brought into mesh with the gear
to be tested. The movable slide carries a rod A, which makes

GAGING AND INSPECTION

contact with a rod B, the latter operating an indicating needle
C through a multiplying lever arrangement. When the center
distance as well as the concentricity of the gear is to be tested,
the movable slide is set to the required center distance by
means of a vernier scale on the bed; then when the gears are
rotated, any inaccuracies in cither the center distance or con-
centricity are noted on the scale over which the indicating
needle moves. If it is desired to test concentricity only, no
attention is paid to the vernier, and the gear to be tested is
kept in contact with the master by a spring, not shown, the
I latter being rotated and the fluctuation of the needle noted.

Another simple but accurate fixture for testing the pitch
diameter and concentricity of spur gears is shown in Figs,
lo and II. The fixture consists of a cast-iron base upon which
two accurately fitting sUdes are held, each shde being pro-
vided with a stud for holding the gears to be tested. The
right-hand slide is moved by means of a long adjusting screw,
while the left-hand slide has only a limited movement, but
transfers its motion greatly magnified to the indicating needle
shown. The sectional view. Fig. ii, shows how the motion
is transferred to the indicating needle, which measures the
difference in concentricity and errors in mesh to 0.0004 inch.

GAGING GRARS 265

To detect errors in concentricity, it is most convenient to
place the gear to be tested on the spindle carried in the left-
hand slide, and to use a blank with a single tooth on the other.
This single tooth is then meshed in succession with all the teeth
of the gear under test, and by observing the different positions
of the indicating needle, it is possible to determine errors in
eccentricity with great accuracy.

Another spur gear testing fixture differing only in a few
minor details from that shown in Fig. 9 is illustrated in Fig.
12. This fixture comprises a base A carrying a slide B on
which a stud is mounted for holding the gear C to be tested.

Fixtnia tor Teitlng Concentricity of TruumiBslon Geari

The master gear D is carefully ground all over, and is held
on a fixed stud on a projecting boss of the fixture. Slide B
is adjusted by a screw to bring the gears into mesh, the screw
being a sliding fit in the boss E of the fixture. This screw
carries a washer as shown, and between the washer and boss E
is a stiff open-wound spring which serves to keep the gears
in mesh with the required tension. The movement of slide B,
which indicates irregularities in the teeth or lack of concen-
tricity, is read off on the dial test indicator F, mounted as
shown and operated by a bracket adjustably mounted on the
movable slide B. Transmission gears for automobiles are gen-
erally made with a maximum eccentricity of 0.003 inch.

Power-driven Gear Testing Fixture. — Another gear testing
fixture for automobile transmission and timer gears is shown

266

GAGING AND INSPECTION

in Fig. 13. In this case the fixture is power-driven. It con-
sists of a cast-iron plate A ribbed at the bottom and machined
on the top surface; a cast-iron plate B with a projecting arm
C on which is secured a shoulder stud D; a cast-iron segment
plate E drilled and reamed at one end to fit fulcrum stud D,
and having at the opposite end a shoulder stud F on which
revolves a master gear of the same pitch as the gear to be
tested; an indicator pointer G drilled to pass down over ful-
crum stud D and axle stud F; a graduated brass plate / secured

to the base A ; and a shaft /, the lower end of which revolve
on a stud beneath the plate B. To this shaft is secured a
worm-wheel, and on the part which projects above this worm-
wheel the gear to be tested is rigidly secured by means of a
key.

The worm L Is made of machine steel, casehardened, and is
driven by a ^-inch half-round belt passing over pulley Af.
A steel spring N is fastened to plate B and index hand G.
The segment plate E is machined on its bottom face, which
slides on the upper face of plate B. On the upper face of
plate E rests the index band, and on top uf this is a steel

GAGING GEARS 267

washer around axle stud F. On this washer rests the master
gear, which is perfect in every respect. The gear to be tested
is revolved by power in the manner indicated, and any irregu-
larity in the diameter is shown on the graduated plate.

Fixture for Testing Transnussioa Gears. — A gear testing
fixture designed especially for testing transmission gears and

jrg

Fig..

capable of adjustment so that it can handle various sizes is
shown in Fig, 14. The gear to be tested is held on a bushing
provided with a squared shank, which is inserted in the holder
A ; this holder is provided with a corresponding square hole
and held in the fixture by means of plate B. An ejecting
mechanism comprising a handle, as shown, is provided for

F«S8 GAGING AND WSPECTION

r raising the spindle of the arbor out of the bushing when it is
dc&ircd to remove the latter. The testing device consists

I primarily of a slide C carrying two teeth of a rack D. The
latter is held to the sUde by means of screws, as shown, so that
it can be removed and rack teeth of the desired pitch and shape
substituted to suit the work to be handled. The testing is
done by means of a test indicator which is held on bracket
E. This indicator is constructed somewhat differently from
that ordinarily supphed, the shank being cut off short and
the multiplying lever F bearing against pin G, which is driven
into movable slide C. A handwhcel H attached to a shaft
which carries a pinion / meshing in a rack in the lower sur-
face of ihc slide is used for adjusting it back and forth to

Fig. IS- Fiiluie tor TsEling Concentricity ol PinioD Sh«ft

suit the size of gear beii^ tested. When testing the gear,
after the latter has been placed on the arbor and the arbor
inserted in the hole in the bushing A, handwheel H is also
operated to bring the rack teeth D in contact with the gear.
The gear is then rotated by hand and the movement of the
indicator A' noticed, and if the gear runs out more than ±0.0015
inch, it b rejected. The indicator is set by means of a ground
master gear.

Fixture for Testing Concentricity of Pinion Shafts. — An in-
teresting fixture for testing the concentricity of pinion shafts
is shown in Fig. 15. This fixture has a base A carrying a tail-
stock and headstock B and C, respectively; in tailstock B is a
rigid center, and in headstock C, an indicating center. The

GAGING GEARS 269

pinion shaft E to be tested is mounted on these two centers.
Located in a plane at right angles to the slide of the main body
of the fixture is a slide F, wiiich carries the master gear G and a
dial indicator H, The teeth in the pinion are kept in mesh
with the master gear by means of a spring behind slide F. A
bracket on the rear side of the fixture carries a second dial in-
dicator /, the spindle of which is brought in contact with the
ground bearing of the pinion shaft. The third indicator pro-
jecting from the headstock at / and shown in detail In Fig. 16
■ is of the multiplying lever indicating type. As shown in Fig.
bt6, this indicator is supported by a sleeve A, which is made a

Fig. 16. Details ol Multipl^iag Lever Indicatoi J, Fig. is

good fit for the hole in the headstock C, Fig. 15. It carries a
cone-pointed bushing B, which projects from the headstock,
the pinion shaft being tested having a hole so that the cone
bushing supports it on the opposite end from the rigid center.
The cone-center in the hole has been ground by locating the
pinion shaft from the bearing at the rear of the pinion. Sleeve
A, Fig. 16, is slabbed down on the front end and machined to
carry the indicating needle C. This, as shown, carries an in-
dicator point D, which can be adjusted to suit the diameter of
the hole in the work and is locked by the nut shown. The
rear end of needle C is pointed and moves over an index plate E,
which is providetl with graduations spaced 0.069 inch apart.
The multiplying lever has a ratio of J to 8| inches, or 69 to i, so

GAGING AND INSPECTION

rtiiat each graduation on the scale represents o-ooi inch error in
the work. The limits on this part are: Concentricity of pitch
circle of teeth, ±0.0015 inch; limits for eccentricity of bearing,
±0.0005 inch; and limits for eccentricity of hole, ±0.0005 ii^ch-
In operation, the pinion E, Fig. 15, is located between the
centers, screw K being adjusted to eliminate end play between
the centers. The pinion shaft is then rotated in mesh with the
master gear, and the various indicators show the following
results: Indicator H tests the accuracy of the pitch diameter

and spacing of the teeth; / tests the concentricity of the bear-
ing in relation to the hole; and J tests the truth of the hole in
relation to the shank bearing diameter. In this way, each
important part of the pinion shaft may be tested to accurate
limits.

Precision Spur Gear Testing Fixture. — Fig. 17 shows a pre-
cision gear testing device for spur gears. It tests the following
elements of the gear: Pitch diameter; truth of pitch diameter
with hole; thickness of teeth on the pitch line; and parallelism
of teeth with axis of gear. In this lixture, revolving stud A is

GAGING GEASS

mounted in a fixecl position and forms a basis from which the
principal dimensions are checked. The removable plug B,
which is mounted on the sliding block C that slides in the ways
D, is located in relation to stud A by the locating pin E. Blocks
C and F are connected by two bolts, only one being visible in the
illustration. One end of the bolts is screwed into block C,
while the other end is a free fit in block F. The blocks are
normally separated by two springs on the bolts, the function
of which will be explained later.

The indicating mechanism G is located in relation to plug B
by the vernier H. The scale of the vernier is fastened to block
C, while the vernier is fastened to part /, making it integral
with the indicating mechanism. The vernier and indicating
mechanism are adjusted by nuts K. The part J is secured in
the T-slot by the nut directly below it, and is adjustable along
the slot, which extends the full length of the fixture. The
indicating mechanism and vernier are locked by nuts L; the
indicating mechanism is adjusted vertically on the pillars M
and secured by thumb-screws N.

In operation, a master gear is placed on driving stud A, and
the gear to be tested on plug B, being free to revolve on the
latter. The locating pin E is then inserted in the proper hole
along the edge of gib 0, thus locking block F securely and lo-
cating the two blocks in the proper relation to each other. The
gear is now revolved by the master gear, which is rotated by a
handle on the squared end of the stud. The indicator then shows
if the teeth arc concentric with the hole, and if the pitch diameter
b correct. While block F is locked to gib 0, block C is free to
move within certain limits. This movement is indicated on
dial P by the multiplying levers. If the gear is out of round,
block C will slide back and forth against the tension of the
springs, thus imparting movement to the indicating lever.

The removable gage Q, for measuring the thickness of the teeth,
is held against them by spring tension; any variation wiU then
be shown upon the dial by means of the multiplying lever. For
testing the parallelism of the teeth and axis, the mechanism is
slid up or down along the pillars M. The indicating needles

GAGING GEARS 273

are set at zero by means of a carefully machined and checked
master gear, prior to testing the gears.

Fixture for Testing Involute Curve of Spur Gear Teeth. —
Many interesting devices have been developed for testing spur
gears, especially the shape of the involute curve of the teeth.
One method consists in rolling the spur gear in contact with a
master and determining whether it is correct or not by the " feel."
Another interesting device, which is shown in Fig. iS, deter-
mines the shape of the involute curve in such a manner that the
amount of error can be read off on an indicator in thousandths
of an inch. This device has a base A in which a dovetail sUde
B is operated by handle C. This slide has a carefully machined
slot in its top face in which a disk D rotates. Disk D is attached
to a spindle E, which carries the gear to be inspected, and, in
addition, two hardened, ground and lapped disks F and C
These disks nm on straightedge B and are made equal in diame-
ter to the base circle from which the involute curve on the gear
teeth is laid out. Located at right angles to slide B is a second-
ary slide / that carries the indicating mechanism. This slide
has a rack attached to its lower surface connecting with the
segment gear J that is operated by handle K. For testing the
accuracy of the involute curve, the gear, together with the two
disks, is rolled along the straightedges and the teeth are brought
into contact with the tooth pointer L of the multiplying lever
J/. This lever transmits a movement to the needle of the in-
dicator. The multiplying lever has a ratio of 10 to i and the
indicator is graduated in thousandths of an inch, so that each
graduation on the indicator represents o.oooi inch variation in
the shape of the curve. One objection to this device is the
shape of the indicator pointer L. Instead of being rounded,
this should be made to a sharp pouit so as to trace the involute
curve without introducing any error.

Another use of this testing fixture b to determine whether or
not the teeth of the gear are in line with the axis. To make this
test, the gear and the member to which it is attached are held
rigidly on the straightedges. Handle K is operated so that
slide / is moved back and forth, passing the indicator point

274

CAGING AND INSPECTION

across the face of the tooth, and in line with the axis. In this
this way the straightness of the tooth surfaces in relation to the
axis of the hole in the gear can be accurately tested.

MacCord Odontoscope for Testing; Gear Teeth Involute
Curve. — Another system for testing the truth of involute curves
is by means of the MacCord odontoscope, shown in Fig. ig.
By this method it is possible to test the accuracy of the involute
curve to a nicety. The fixture has two templets A and B which
are cut out of fairly thick sheet metal and correspond to the
teeth of a pair of gears. These templets are secured to arms

==e^.

"" ^^\^v

/""^

^J^\

^>|\\

/ ■n't

\f~)-

~-^m~^f^^

>-v

c \

ilJ^ \

turning about the axes C and D, the distance between which is
adjustable. Shaft D carries a graduated segment K, which may
be slowly rotated by arm L and screw E, or any other equivalent
device. Motion is thus communicated to C, the teeth A being
kept in contact with 5 by a light weight or spring, not shown.
Cylindrical barrels F and G are accurately turned to the same
diameter as the pitch circle from which the involute curves are
struck off; F is fixed on the axis C, while G carries a pointer H
that turns freely on axis D and is connected by a spring, not
shown. The tendency is to wind up on barrel G the fine dexible
wire /, which is secured to both barrels in the manner of a

GAGING GEARS

cross belt. Therefore, barrels F and G turn in opposite direc-
tions with a constant velocity ratio. The velocity ratio of C
and D, however, is determined by the templets A and B that
will not remain in mesh unless the contour of the teeth is strictly
conjugate. While turning the tangent screw in one direction or
the other, it is possible to examine the action during the arc of
approach or retreat of the teeth, and if the templets are cor-
rectly formed, the segment A' and pointer H will move at the
same rate and in the same direction, so that, if the pointer is set
at zero in the graduated arc, it will remain at zero throughout the
action, any movement indicating an inaccuracy in the shape of
the involute curve. For actual work the sensitiveness of the
involute is increased by introducing multiplying gears between
barrels F and G, thus producing a greater deflection of needle
H for a given magnitude of error, and causing minute errors to
be indicated.

Testing Spur Gears for Noise under Load. — After the gears
are cut and inspected for other defects, they are generally sub-
jected to a noise test. In making this test, it is the general prac-
tice to holt! the gears to be tested in some sort of fixture in which
a load can be applied while the gears are running at high speed.
It is also customary to have the load either approximate or exceed
that which will be carried by the gear under actual working con-
ditions. Fig. 2o shows a gear testing fixture for spur gears which
embodies the features just mentioned. This consists of a base
carrying three slides. The slides at the rear, which are guided
by ways on the bed, are held accurately in line with each other
and are gibbed to the bed. The right-hand bracket carries
a dead center and the left-hand bracket, a driving center, ro-
tated by the pulley shown. The gear to be tested is held on a
mandrel and b in mesh with another gear held on a spindle
that rotates in bronze bearings. The outer end of this spindle
carries a disk and band brake.

In operation, She gear to be tested is located as shown, and the
gear on the spindle is brought into mesh with it by the hand-
lever at the front of the machine. The power is turned on
slowly at first and then gradually increased. At the same

376

GAGING AND INSPECTION

time the band is tightened on the disk to increase the power
required to rotate the gear on the spindle. The operator mean-
while observes closely the noise produced. If it makes a hum-
ming sound, the gear is all right, but if It makes an intermittent
noise or clash, it indicates thai the teeth are unevenly spaced,
eccentric with the hole, or incorrectly formed.

Testing Bevel Drive Ring Gears. — Several methods are em-
ployed for testLQg bevel drive ring gears for automobile trans-
missions. One of the most important tests is to determine
within fixed limits the relation of the teeth to the back face and

Fixtarc for Teiting Spur Ge«rt tot IToise under Load

hole. In the helical type of ring gear this is generally accom-
plished by what is known as a " ball test." The ring gear to
be tested is fastened by the bolt holes to a carefully ground ring,
which forms a part of the fixture and is free to rotate. The in-
specting is done by means of a dial test indicator held in an arm,
in the lower or measuring end of which is a carefully ground and
lapped ball that is brought in contact with the teeth being tested.
The spindle carrying the ball is kept in contact with the gear
teeth by means of a stiff spring, and the ball is raised up out
of contact with the teeth by a lever. The spaces between the
teeth are tested in this way after the gear has been hardenedi 1
and the gear is allowed to run out about 0.003 inch.

GAGING GEARS

177

Testing Ground Faces of Bevel Ring Gears. — In grinding
the rear face of a bevel ring gear, it is the usual practice to
locate the gear from the pitch line of the teeth by means of
accurate balls. After the front and rear faces and hole have
been ground, the gear is tested in the manner shown in Fig.

21. The fixture here shown consists of a cast-iron base A
to which a hardened and ground steel ring B is fastened. In
the top face of this ring are carried steel balls on which the
gear rests. The ring gear is located from the hole by a hard-
ened and ground stud C, which is fastened to the cast-iron
base. The test for truth is accomplished with the test indi-

278

GAGING AND INSPECTION

cator D held in the bracket E. Bracket E is tree to swing
about the stud on which it is mounted when the clamp shown. '
is released. The inspector, in testing for truth, rotates the
gear on the balls as shown in the illustration, and at the same
time watches the movement of the indicator needle to see if '
any inaccuracy has been caused by the grinding operation.
As extreme accuracy in this part is necessary, a duplicate fix-
ture is used in the grinding department by the operator (the |
one who grinds the inside face of the gear) to determine if the I

final grinding operation is correct before the gears leave the j
grinding department.

Testing Bevel Gears for Noise. — Bevel gears are subjected |
to a noise test in a similar manner to that described in con- 1
nection with transmission gears. Several devices have been
developed for the purpose, one of which is shown in Fig. 22.
This is made from a discarded Lincoln tj-pe milling machine.
The testing fixture comprises two brackets held on the table,
and a special holder on the spindle for the ring gear. The |
brackets A and 5, which carry centers for supporting the pinion I
arbor, are held to the special table C by T-bolts and nuts. The J

GAGING GEARS

279

bracket A is provided with a wing-nul, so that it can be easily
removed to insert the work. The ring gear k held in a manner
similar to that employed in the Gleason bevel gear generator,
being located from the front inside face by a shoulder plate D,
to which the gear is bolted. Spring pins located in the special
faceplate E are also used to support the rim of the gear. The
machine is provided with a special hardened and ground spindle
on which the ring gear fixture is retained. The spindle is
hoUow and a pull-rod passing through it is used to clamp the
gear and shoulder plate D up against the fixture. To the rear
end of the spindle is attached the handle F, which is used to

Fig. 13. Spacial Fixture

rotate the ring gear that meshes with the pinion held on the
arbor. The operator brings the ring gear and its mating
pinion into mesh, and then rotates the handle F slowly, listen-
ing carefully to find out at which points of the rotation noise
is produced or where the teeth bear hard. In addition to this,
the ring gear and mating pinion are given a noise test under
load, while being rotated at a high speed.

Testing Running Action of Bevel Gears. — A bevel ring
gear and pinion must be accurately mounted to give satis-
factory results, and in order to determine whether the gear
will run correctly or not when mounted, it is advisable in most
cases to test the gear under actual working conditions in a
special fixture that has been designed for the purpose, and so

GAGrNO GEARS 381

arranged that any errors in the gear are magnified. A simple
testing device which gives satisfactory results is shown in Fig.
33, and consists of a base A upon which is mounted an adjust-
able bracket B that carries the bevel pinion, and a bracket
C that carries tJie ring gear. The pinion shaft D is driven
by a worm-wheel E, which, in turn, receives power from a worm
held on shaft F. the latter being rotated by handwheel G. The
bevel ring gear is mounted so that it is free to be rotated by
the pinion. Located on the spindle to which the ring gear
is attached is a fine-pitch spur gear H which meshes with a
pinion held in a bracket /. The ratio between this spur gear
and pinion is 10 to 1 . Located on the pinion shaft is a pointer
/ which rotates around the graduated dial K, the latter being
attached directly to the bracket /.

In operation, the pinion and bevel ring gear are carefully
mounted and then handwheel G is rotated at a uniform speed.
If the bevel pinion and riag gear are properly cut and in cor-
rect mesh, the indicator / wilt travel over the dial K with a
steady, uniform motion. On the other hand, if the meshing
is incorrect, the pointer will move over the dial with a jerky,
irregular motion. The block B carrying the horizontal pinion
shaft is adjustable so that the gears can be made to mesh in-
correctly in order to study the effect of this action. The fix-
ture is so designed, h{)wev(.T, that there is one correct position
that cannot be varied more than o.ooi inch.

Testing Fixture for Steering Worm Sectors. — Fig. 34 shows
a testing fixture which is used for determining the amount
of eccentricity of a steering worm sector, as used on the Cadillac
motor car. This particular steering worm sector is made
eccentric so that, by adjusting an eccentric bushing, any wobble
can be taken up in the steering sector until it has been worn
down to an "equal radius." The teeth on this sector are not
concentric with the shank, and as they wear more in the center
than at either end, this allowance for adjustment is necessary.
In order to check the amount of eccentricity on this sector,
a special testing fixture has been devised as shown in Fig. 24.
Here the steering worm sector is shown, by heavy dotted lines,

382

GAGING AND INSPECTION

mounted in two V-blocks and held just tight enough to prevent
any lost motion, by means of a toe-clamp A and a nut B. The
sector is then swung aroimd past the rack tooth C, which .
meshes with the teeth in the sector. The amount that the
center of the worm is eccentric with the two extreme ends of
the sector is then determined accurately by means of the dial

test indicator D. which is acted upon by the pin E held in the
slide F. This slide is moved up against the tension of spring
H by pulling on button C

Fixture for Testing Center Distance of Steering Sector and
Worm, — After the amount of eccentricity of the worm sector
has been tested in the fixture shown in Fig. 24, the next step

GAGING GEARS 283

■

is to test the center distance of the worm in connection with
the sector,- working the latter on the high point, as indicated
in Fig. 25. The worm is held on a shaft A provided with a
key for driving it, this shaft being rotated by handle B. The
sector is held in a swinging member or arm C operated by
handle D, The worm is placed on shaft A^ sector E is then
placed in swinging arm C, and the latter is swung in imtil the
sector meshes properly with the worm. From time to time,
this fixture is tested and set by a master sector and worm and
then a reading is taken on the dial test indicator F. When
the work being tested is put in this fixture, the needle must
indicate within ±0.001 inch of the zero point registered by the
master. In order to see that the worm is not eccentric, it is
rotated by means of handle 5, and as the swinging arm C is
only held in by means of the hand, the eccentric movement
of the sector is easily noticed, if the arm is forced back by the
rotation of the worm. This gives an indicating reading on
the dial test indicator, and the amoimt of eccentricity may
also be determined in the same fixture.

INDEX

Page

Allowance 30

for various classes of fits 36, 39

to compensate for errors in pitch of screw threads, table 204

American Society of Mechanical Engineers' gaging devices 248

Ames dial indicator 118

Angle of thread, testing 238

tolerances 206

Anvil type and ball-point thread micrometers compared 228

A. S. M. E. gaging devices 248

Automatic comparator, Hartman 23

Ball bearing race rings, gaging and inspecting 177

Ball bearing rings, annular, gaging raceways in 179

Ball bearings, gaging and inspecting 166

standard sizes and tolerances for ball bearings, S. A. E., table 174, 17$

testing concentricity of 182

testing external diameter of 183

Ball gaging machines, automatic 171

Ball-point and anvil type thread micrometers compared 228

Ball-point micrometer 219

Balls, gaging and inspecting 166

gaging with Hirth minimeter 171

Bench micrometer caliper 4

Bench type measuring machines 5

Bevel drive ring gears, testing 276

Bevel gear blanks, templets for 255

testing with bevel protractor 256

Bevel gears, testing for noise 278

testing running action of 279

tolerances 260

Bevel protractor for testing bevel gear blanks 256

Bevel ring gears, testing ground faces of 277

Bicknell-Thomas thread lead indicator 237

Blocks, reference 2

reference, Johansson 3

Bolt of Ross rifle, gaging 103

Bolts, tolerances for, British standard Whitworth screw threads, table 202

Box inspection gage for generator frame 187

Box type inspection fixtures 184

Briggs pipe thread gages 215

285

286 BRITISH — ELEMENTS

Page

British standard pipe threads 214

British standard Whitworth screw threads — tolerances for bolts and nuts,

tables 202, 203

Brown & Sharpe measuring machine 6

Built-up limit snap gage 70, 71

Built-up templet gage 93

Caliper, bench micrometer 4

gear tooth 257

Caliper type dial indicator 124

Camshaft gage, electrical : . . . 156

multiple indicating 155

Camshaft, inspecting cams on gas engine 151

Cams, ignition, electric starter, device for testing 157

on gas engine camshaft, inspecting 151

Cartridge chamber in rifle barrel, progressive gaging of 97

Center distances, of spur gears, testing 261

of steering sector and worm, testing fixture for 282

Clearance 31

Combination or progressive gages 95

Comparator, automatic, Hartman 23

indicating, for testing lead of taps and screws 231

Concentricity and radial position of cutter teeth, testing 147

Concentricity gages 143

for shells 149, 150

Concentricity of ball bearings, testing 182

Concentricity of gear blanks, testing 146

Concentricity of pinion shafts, fixture for testing 268

Concentricity of spur gears, testing 262

Cutter teeth, testing concentricity and radial position of 147

Cylinder gage, gas engine 130

Depth gage, indicating 137

Dial and needle gage no

Dial indicating gages 117

Dial indicator, for testing lead of taps, Wolfe 233

for testing pressure 162

of caliper type •. 124

Die chasers, inspecting 246

Disk t>Tx; reference standard 2

Dowel-pin holes, gaging milled surfaces in relation to 185

Drawings, methods of giving limits on 41

Drive fit 39

Driving fits, tolerances for, table 38

Electrical camshaft gage 156

Electric starter ignition cams, device for testing 157

Electroplating gages 87

Elements of screw threads 198

END-MEASURING — GAGES 287

Pack

End-measuring rod 2

Engineering Standards Committee, tolerances on included angle of screw

threads, table 206

Escapements, watch, gaging 191

Extractor of Ross rifle, gaging 105

Feeler gages io6

Feeler plug, for determining pressure between measuring points 9

"Field" inspectors for gages. . . . '. 54

Fit allowances 36

Fit, drive 39

driving, tolerances for, table 38

establishing allowances and tolerances for 39

force 39

force, tolerances for, table 39

push 38

push, tolerances for, table 37

running 38

running, tolerances for, table 37

Fixed gage 50

Fixture, for testing concentricity of pinion shafts 268

for testing involute curve of spur gear teeth 273

for testing spur gears 27b

for testing steering worm sectors 281

for testing transmission gears 267

gear-testing, power-driven 265

inspection box type 184

Flush-pin gages 106

Force fit 39

tolerances for, table 39

G^cs, box inspection, for generator frames 187

Briggs pipe thread 215

care used in applying 59

concentricity 143

concentricity, for shells 149, 150

conditions under which they are used 54

cylinder, gas engine 130

dial indicating 117

electrical camshaft 156

electroplating 87

feeler 106

fixed 50

flush-pin 106

for screw machine work 78

grinding and lapping 84

indicating 106

indicating, application of 134

288 GAGES

Page

Gages, indicating, dq)endinig upon sense of hearing 163

indicating, employing sense of touch 106

indicating, for inspecting lead and pitch diameter 24$

indicating, for testing shrapnel shells 140

indicating height and depth 137

indicating sight no

indicating thickness 141

influence of condition of work on wear of 55

Ijfe of S3, SS

life of, condition of measuring surface 57

life of, used for high-explosive shells 58, 59, .60

limit, for measuring recessed work 80

limit, inspection room 82

limit, making 83

limit snap and plug, for threaded work 241

limit snap, built-up type 70, 71

limit snap, for testing lead and pitch diameter 242

limit snap, rapid inspection 69

material for $6

micrometer in

micrometer indicating 124

microscope 111

multiple indicating camshaft 155

multiplying lever indicating no, 112

needle and dial no /

plug and snap, limit working and inspection 50

plug, types of 61

profile 89

progressive or combination 95

reference 47> 48

reference thread 210

reference thread, tolerances on 207

reference, tolerances 49

ring and plug, taper 72

snap, tyjjes of 67

standard 67

standard, erroneous use of 50

star 131

taper pin 78

taper plug and ring, types of 76

taper, setting limits on 73

templet 89

templet, built-up type 93

thread, limit working and inspection 239

three-point indicating 127

tool-setting, advantages of S3

" touch-type " 107

working and inspection tolerances 51

GAGING — HOLES 289

Pace

Gaging and inspecting ball bearing race rings 177

Gaging and inspecting ball bearings 166

Gaging and inspecting balls 166

Gaging balls with Hirth minimeter 171

Gaging bolt of Ross rifle 103

Gaging devices, A. S. M. £ 248

Gaging extractor of Ross rifle 105

Gaging gears 254

Gaging milled surfaces in relation to d6wel-pln holes 185

Gaging, ordinate system 158

progressive, of cartridge chamber in rifle barrel 97

progressive, of screw machine products 98

Gaging raceways in annular ball bearing rings 179

Gaging raceways in thrust bearings 179

Gaging screw threads 198

Gaging shoulder distances *. 94

Gaging taper on rifle barrel 102

Gaging watch escapements 191

Gas engine camshaft, inspecting cams on 151

Gas engine cylinder gage 130

Gear blanks, inspecting 254

testing concentricity of 146

Gears, bevel drive ring, testing 276

bevel ring, testing ground faces of 277

bevel, testing for noise 278

bevel, testing running action of 279

bevel, tolerances for 260

gaging and inspecting 254

spur, testing center distances of 261

spur, testing for noise under load 275

spur, testing pitch diameter and concentricity 262

spur, tolerances 259

transmission, fixture for testing 267

Gear teeth, MacCord odontoscope for testing 274

Gear-testing fixture, power-driven 265

Gear tooth caliper 257

Gear tooth templets 256

Generator frame, box inspection gage for — , '. 187

German type of measuring machine 21

Grinding and lapping gages 84

Hartman automatic comparator 23

Height and depth gages, indicating 137

High-explosive shells, concentricity gage for 149

life of gages used for 58, 59, 60

Hirth minimeter 115

for gaging balls 171

Holes, tolerances for, table 36

290 INDICATING — JOHANSSON

Page

Indicating comparator for testing lead of taps and screws '231

Indicating gages 106

application of 134

depending upon the sense of hearing 163

dial 117

employing sense of touch 106

for inspecting lead and pitch diameter 245

for testing 'shrapnel shells 140

micrometer 1 24

multiplying lever 112

three-point 127

Indicating height and depth gages 137

Indicating sight gages no

Indicating thickness gages 141

Indicator, dial, for testing lead of taps, Wolfe 233

dial, for testing pressure 162

dial, of caliper type 124

for testing lead of screws and taps, Wells 232

lead test 235

liquid, measuring machine 21

thread lead, Bicknell-Thomas 237

thread measuring, using one wire 222

Inspecting and gaging ball bearings 166

Inspecting and gaging balls 166

Inspecting ball bearing race rings 177

Inspecting cams on gas engine camshaft 151

Inspecting die chasers 246

Inspecting gear blanks 254

Inspecting gears 254

Inspecting lead and pitch diameter, indicating gage for •. 245

Inspecting screw threads 198

Inspection and working thread gages, limit 239

Inspection fixtures, box type 184

Inspection gage, box-type, for generator frame 187

tolerances 51

Inspection plug and snap gages, limit 50

Inspection room limit gages 82

Inspectors for gages, " field " 54

Interchangeable manufacture 29

Interchangeable parts, setting manufacturing limits on 33

Interferometer 24

construction of 27

principle of 25

International Bureau of Weights and Measures i

International meter i

Involute curve, of gear teeth, MacCord odontoscope for testing 274

of spur gear teeth, fixture for testing 273

Johansson reference blocks 3

LAPPING — MEASURING 291

Page

Lapping gages 84 ,

Lead and pitch diameter, indicating gage for inspecting 245

limit snap gages for testing 242

Lead indicator, thread, Bicknell-Thomas type 237

Lead, of screw threads, simple device for testing 230

of taps and screws, indicating comparator for testing 231

Lead test indicator 235

Length unit, standard i

Life of gages, condition of measuring surface 57

used for high-explosive shells, tables 58, 60

Life of plug, ring, and snap gages 53» 55

Limit gages, for measuring recessed work 80

inspection room 82

making 83

reference 48

Limits 30

manufacturing, setting 33

methods of establishing 34

on drawings 41

on taper gages, setting 73

system of, Newall Engineering Co 34

Limit snap and plug gages for threaded work 241

Limit snap gage, built-up type 70, 71

for testing lead and pitch diameter 242

rapid inspection 69

Limit system 29

advantages of 30

applied to gaging of shoulder distances 94

for general work 44

Limit working and inspection plug and snap gages 50

Limit working and inspection thread gages 239

Liquid indicator measuring machine 21

MacCord odontoscope for testing gear teeth 274

Manufacturing limits, setting on interchangeable parts 33

Material for gages 56

Measuring machine, bench type 5

Brown & Sharpe 6

German type 21

liquid indicator 21

Newall 16, 19

Pratt & Whitney 9

principle of 5

Slocomb 12

Swiss type 14

Measuring screw threads, one-wire system of 221

projection method for 253

three-wire method of 223

292 METER — PRECISION

Page

. Meter, international .^ i

Michelson interferometer 25

MiGTometer caliper, bench 4

Micrometer gages 1 11

Micrometer, having ball points 219

thread 217

thread, comparison of ball-point and anvil type 228

Micrometer indicating gages 124

Microscope gages iii

Microscope with illuminated chamber 192

Minimeter, Hirth 115

Hirth, for gaging balls 171

Multiple indicating camshaft gage 155

Multiplying lever indicating gages 112

Multiplying lever type of gage no

Needle and dial gage no

Newall Engineering Co/s system of limits 34

Newall Engineering Co/s tolerances for fits, tables 3^) 37i 38

Newall measuring machine 16, 19

Noise test, for bevel gears 278

for spur gears 275

Nuts, tolerances for, British standard Whitworth screw threads, table 203

Odontoscope for testing gear teelh, MacCord 274

One-wire system of measuring screw threads 221

Parallelism of shafts, testing 154

Pinion shafts, fixture for testing concentricity of 268

Pipe thread gages, Briggs 215

Pipe threads 213

British standard 214

Piston-pin holes, testing with relation to body of piston 145

Pitch diameter, screw thread, indicating gage for inspecting 245

limit snap gages for testing 242

tolerances 204

Pitch diameter, spur gear, testing 262

Pitch, screw thread, allowances to compensate for errors in, table ; 204

tolerances on 204

Plug and snap gages, limit working and inspection 50

Plug, feeler, for determining pressure between measuring points 9

Plug gages, for threaded work, limit 241

life of S3

taper 72

types of 61

Power-driven gear-testing fixture 265

Pratt & WTiitney measuring machine 9

Precision spur gear testing fixture 270

PROFILE — SCREW 293

Page

Profile gages 89

Progressive or combination gages 9$

Projection method of measuring screw threads 253

Projector methods for testing watch escapements 191

Protractor, bevel, for testing bevel gear blanks 256

Push fit 38

tolerances for, table 37

Radial position of cutter teeth, testing concentricity and 147

Recessed work, limit gage for measuring 80

Reference blocks 2

Johansson 3

Reference gages 47

tolerances 49

Reference limit gages 48

Reference or standard gage 67

Reference standards 2

disk type 2

Reference taper plug and ring gages 72

Reference thread gages 210

tolerances on 207

Rifle barrel, gaging taper on 102

Rifle, gaging bolt of 103

gaging extractor of 105

Ring gages, life of 53

taper , 72

Ring gears, bevel drive, testing 276

Rod, end-measuring 2

Roller bearings, sizes and tolerances for, S. A. E., table 176

Running fit 38

tolerances for, table 37

S* A. E. standard sizes and tolerances, for ball bearings, table i74) i75

for roller bearings, table 176

Screw machine products, progressive gaging of 98

Screw machine work, gage for 78

Screws and taps, lead of, indicating comparator for testing 231

Screw thread gages, limit working and inspection 239

Screw thread lead indicator, Bicknell-Thomas 237

Screw thread micrometers 217

comparison of ball-point and anvil type 228

Screw threads, allowances to compensate for errors in pitch, table 204

angle of, testing 238

British standard Whitworth — tolerances for bolts and nuts, tables. . 202, 203

elements of 198

gaging and inspecting , 198

lead of, testing by simple device 230

ii one-wire system of measuring 221

294 SCREW — TEMPLET

Page

Screw threads, pipe 213

pipe, British standard 214

projection method for measuring 253

three-wire method of measuring 223

tolerances 200

U. S. S., tolerances on 206, 208, 209

Shafts, testing parallelism of 134

Shells, high-explosive, life of gages used for S^* 59* 60

Shoulder distances, limit system applied to gaging 94

Shrapnel shells, gage for testing concentricity of 150

indicating gage for testing 140

Sight gages, indicating no

Slocomb measuring machine ', 12

Snap and plug gages, limit, for threaded work : 241

limit working and inspection 50

Snap gages, life of 53

limit, built-up type 70, 71

limit, for testing lead and pitch diameter 242

limit, rapid inspection 69

types of 67

Society of Automotive Engineers standard sizes and tolerances, for ball bear-
ings, tables 174, 175

for roller bearings, table 176

Sodium light used in connection with interferometer 25

Springs, time fuse percussion restraining, device for testing 163

Spur gears, center distances of, testing 261

testing for noise under load 275

testing pitch diameter and concentricity 262

tolerances 259

Spur gear teeth, fixture for testing involute curve 273

Spur gear testing fixture, precision 270

Standard holes, tolerances for, table 36

Standard or reference gage 67

Standards, reference 2

Standard unit of length i

Star gages 131

Steering worm sectors, testing fixture for 281

Surfaces at right angles, testing 136

Swiss measuring machine *. 14

System of limits, methods of establishing 34

Taper gages, setting limits on 73

Taper on rifle barrel, gaging 102

Taper pin gage 78

Taper plug and ring gages 72

t>pes of 76

Taps and screws, lead of, indicating comparator for testing 231

Templet gages 89

built-up 93

TEMPLETS — WORM 295

Pacb

Templets, for bevel gear blanks 255

gear tooth 256

Test indicator, lead 235

Thickness gages, indicating 141

Threaded work, limit snap and plug gages for 241

Thread gages, Briggs pipe 215

reference 210

reference, tolerances on 207

Thread measuring indicator using one wire 222

Threads, see " Screw Threads"

Three-point indicating gages 127

Three-wire method of measuring screw threads 223

Thrust bearings, gaging raceways in 179

Time fuse percussion restraining springs, device for testing 163

Tolerance 30

for angle of thread 206

for bevel gears 260

for bolts and nuts, British standard Whitworth screw threads, tables. 202, 203

for driving fits, table 38

for force fits, table 39

for push fits, table 37

for running fits, tabic 37

for spur gears 259

for standard holes, table 36

for various classes of fits, establishing 39

for wear S3

on pitch and pitch diameter of screw threads 204

on reference gages 49

on reference thread gages 207

on screw threads 200

on U. S. standard screw threads 206, 208, 209

on working and inspection gages 51

Tolerances and sizes for ball bearings, S. A. E., table i74. I7S

Tolerances and sizes for roller bearings, S. A. E., table 176

Tool-setting gages, advantages 53

" Touch-tyi>e " gages 107

Transmission gears, fixture for testing 267

Unit of. length, standard i

U. S. standard screw threads, tolerances on 206, 208, 209

^Vatch escapements, gaging 191

Wear of gages, tolerances for 53

Wells indicator for testing lead of screws and taps 232

Whitworth screw threads, tolerances for bolts and nuts, tables 202, 203

Wolfe dial indicator for testing lead of taps 233

Working and inspection gages, tolerances 51

Working and inspection plug and snap gages, limit 50

Working and inspection thread gages, limit 239

Worm sector, steering, testing fixture for 281

UbI XO I

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